mesa: add support for CET to x86/x86-64 asm files.

mesa: add support for CET to x86/x86-64 asm files.

Control-flow enforcement technology is a new instructions on x86
processors to denote where indirect jumps can land. Gcc auto adds
the instruction (which encodes as a NOP on older CPUs) to entrypoints
but assembler files need manual adding. This adds it to all the
entry points in the mesa x86/x86-64 assembler files.

This will only happen if mesa is built with the -fcf-protection flag
to gcc as some distros are wanting to do.

Acked-by: Eric Anholt <eric@anholt.net>