Implement the fpu_kern(9) KPI on arm64

[andrew]

Summary

Add support for the fpu_kern(9) KPI for arm64. It hooks into the existing
VFP code to store the old context, with lazy loading of the new context
when needed.

FPU_KERN_NOCTX is missing as this is unused in the crypto code this has
been tested with, and I am unsure on the requirements of the UEFI
Runtime Services.

[kib]

sys/arm64/arm64/trap.c

285

You might add an assert in do_el0_sync() that pcb_fpflags has PCB_FP_KERN cleared and that pcb->pcb_fpusaved == &pcb->pcb_fpustate. There, you probably want to assert !=.

sys/arm64/arm64/vfp.c

246

You initialize the new kernel vfp save area with zeroes. This includes the vfp_fpcr and vfp_fpsr values loaded on vfp access. Are 0's the correct values there ?

sys/opencrypto/crypto.c

1249

This change is not needed yet ? There is no arm64 files added to aesni module.

[kib]

The fpu_kern(9) man page should be updated, with a note that arm64 is included in the supported arches.

[andrew]

sys/arm64/arm64/trap.c

285

I thought I did, but seem to have lost that change.

sys/arm64/arm64/vfp.c

246

The kernel only ever initialises fpsr and fpcr to 0.

sys/opencrypto/crypto.c

1249

There will be soon, I have the code ready, just need the last bits of clean up. I included this with this change so some of the code would be tested.

[andrew]

sys/arm64/arm64/trap.c

285

I added the PCB_FP_KERN check in rS307565 as it's not in the user mask.

[andrew]

Update the manpage
Add a KASSERT to the end of do_el0_sync