arm64: turn el0 EXCP_UNKNOWN into a SIGILL

[emaste]

Summary

It seems we get EXCP_UNKNOWN from QEMU when executing zeroed memory. Print a register dump here and signal illegal instruction. Also print a register dump for other invalid exceptions, before panic.

[emaste]

sys/arm64/arm64/trap.c

241–244

oops, meant without the -, so that we get:

  x0:       7ffffff680
  x1:                0
  x2:               14
  x3:                8
  x4:                0
  x5:                1
...