Add retguard to macppc kernel locore.S, ofwreal.S, setjmp.S

This changes RETGUARD_SETUP(ffs) to RETGUARD_SETUP(ffs, %r11, %r12)
and RETGUARD_CHECK(ffs) to RETGUARD_CHECK(ffs, %r11, %r12)
to show that r11 and r12 are in use between setup and check, and to
pick registers other than r11 and r12 in some kernel functions.

ok mortimer@ deraadt@

Retguared asm macros for powerpc libkern

This was in the macppc snap, but I forgot to include it in my last
commit "Retguard asm macros for powerpc libc, ld.so"

Provide an optimized implementation of ffs(3) in the kernel on
arm64/powerpc/powerpc64, making use of the count leading zeros
instruction.

powerpc testing by cwen@; ok kettenis@ deraadt@

Retguared asm macros for powerpc libkern

This was in the macppc snap, but I forgot to include it in my last
commit "Retguard asm macros for powerpc libc, ld.so"

Provide an optimized implementation of ffs(3) in the kernel on
arm64/powerpc/powerpc64, making use of the count leading zeros
instruction.

powerpc testing by cwen@; ok kettenis@ deraadt@

Provide an optimized implementation of ffs(3) in the kernel on
arm64/powerpc/powerpc64, making use of the count leading zeros
instruction.

powerpc testing by cwen@; ok kettenis@ deraadt@