Fixes for X on PowerPC

[Nathan Whitehorn]

I was just bootstrapping a new (to me) laptop and ran into some minor 
difficulties getting X running. They can be fixed with the patch at 
http://people.freebsd.org/~nwhitehorn/new_xorg_ppc.diff

It has the following parts:
1. plist fix for graphics/libdrm (the Intel driver is only built on x86 
platforms)
2. only apply MMX/SSE2 flags in configure on platforms that have MMX and 
SSE2 for x11/pixman to avoid errors from configure
3. Use old ATI driver on platforms without KMS (for now, everything but x86)
4. Fix error in xorg-server makefile EXTRA_PATCHES where some 
platform-specific patches would replace rather than add to the patches list.

The only even vaguely substantive change is the last patch:
5. xf86EnableIO() and xf86OpenConsole() no longer seem to be called in 
the same order, with the result that xf86Info.consoleFd hasn't been set 
yet when xf86EnableIO() is called. I've copied what Linux does here and 
used /dev/mem instead, as well as copying Linux in making errors there 
non-fatal. Incidentally, the xf86EnableIO() implementation is one of the 
shadiest and most questionable things I have ever seen. I really doubt 
it does whatever it is meant to do correctly, but it at least does the 
same thing old Xorg did now.
-Nathan