RFC: HW watchpoints and single stepping for ARMv6/v7

[Zbigniew Bodek]

Hello,

We would like to add HW watchpoints and HW single step support to ARMv6 kernel.
Please check this review: https://reviews.freebsd.org/D4037

Since there are differences between debug architectures on ARM (v6,
v6.1, v7, v7.1) I would like to ask for some testing on your machines.
I was able to test this on Pandaboard and Arndale but please check
whether this works on your targets as well.

Rise a red flag if you see any issues or in worst case scenario -
"undefined instruction" error.

Best regards
zbb