Attempt to fix build breakage in r344458.

Non-x86 arches use an inconsistently named header for the file containing
"pc" attributes, and the ifdef messes to include the right header were out
of date in the 2 files that I added to the MI files list.

Only amd64, arm, i386, mips, powerpc and sparc64 are supposed to support
syscons. Only arm and mips were out of date in the ifdef. Test
coverage for of syscons in arm is broken (turned off) in NOTES, but
syscons is in some other arm config files which universe detects as broken.
arm64 and riscv remain broken due to the opposite bug of not turning off
sc in NOTES, the same as before r344458 (see r344443).

The header is MD to contain possibly-non-"pc" encodings of attributes, but
since the attributes are essentially virtual in graphics mode and non-x86
arches only support graphics mode, the header has always been the same on
all arches except for different style bugs, so there should be only 1 MI
copy of it for syscons' use. It was used in pcvt and still gives an an
API and an ABI, so it should be public and MI near or in sys/consio.h.