Missing .if in usr.sbin/Makefile.riscv

Hi,

for a test (and some fun - okay, somewhat slow one), I did a make
buildworld on my Star64 board. It worked well, albeit a bit slow (at
the moment, I am running from micro SD card, not the quick media
either).

There was a fatal error, trying to build bhyve binary in presence of
WITHOUT_BHYVE in my /etc/src.conf (I do not plan to test bhyve on
Star64 for now, thus I decided to not build it). See:

--- 8< ---------------------------------------------------------------

===> usr.sbin/bhyve (all)
cc -target riscv64-unknown-freebsd15.0 --sysroot=/usr/obj/usr/src/riscv.riscv64/tmp -B/usr/obj/usr/src/riscv.riscv64/tmp/usr/bin -fpie -DPIC   -O2 -pipe -fno-common -march=rv64imafdc -mabi=lp64d   -I/usr/src/sys/contrib/libfdt -I/usr/src/usr.sbin/bhyve             -I/usr/src/usr.sbin/bhyve/../../contrib/lib9p  -I/usr/src/sys -DINET -DOPENSSL_API_COMPAT=0x10100000L -I/usr/src/sys/dev/e1000 -I/usr/src/sys/dev/mii -I/usr/src/sys/dev/usb/controller -fPIE -mno-relax -MD  -MF.depend.acpi.pieo -MTacpi.pieo -std=gnu17 -Wno-format-zero-length -fstack-protector-strong -Wsystem-headers -Werror -Wall -Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wunused-parameter -Wchar-subscripts -Wnested-externs -Wold-style-definition -Wno-pointer-sign -Wdate-time -Wmissing-variable-declarations -Wno-empty-body -Wno-string-plus-int -Wno-unused-const-variable -Wno-error=unused-but-set-parameter -Wno-
 error=cast-function-type-mismatch  -Qunused-arguments      -c /usr/src/usr.sbin/bhyve/acpi.c -o acpi.pieo
/usr/src/usr.sbin/bhyve/acpi.c:54:10: fatal error: 'vmmapi.h' file not found
   54 | #include <vmmapi.h>
      |          ^~~~~~~~~~
1 error generated.
*** Error code 1

Stop.
make[4]: stopped making "all" in /usr/src/usr.sbin/bhyve
*** Error code 1

Stop.
make[3]: stopped making "all" in /usr/src/usr.sbin
*** Error code 1

Stop.
make[2]: stopped making "all" in /usr/src
      950.67 real       303.38 user        63.05 sys
*** Error code 1

Stop.
make[1]: stopped making "buildworld" in /usr/src
*** Error code 1

Stop.
make: stopped making "buildworld" in /usr/src

--- 8< ---------------------------------------------------------------

I realised usr.sbin/Makefile.riscv is problem here, as there is just

--- 8< ---------------------------------------------------------------

SUBDIR+=	bhyve
SUBDIR+=	bhyvectl

--- 8< ---------------------------------------------------------------


while relevant part of usr.sbin/Makefile.aarch64 is

--- 8< ---------------------------------------------------------------

.if ${MK_BHYVE} != "no"
SUBDIR+=	bhyve
SUBDIR+=	bhyvectl
.endif

--- 8< ---------------------------------------------------------------

and I think that's what usr.sbin/Makefile.riscv should contain.

Regards,
Milan