vmm: implement VM_CAP_MASK_HWINTR on AMD CPUs

This patch implements the interrupt blocking VM capability on AMD
CPUs. Implementing this capability allows the GDB stub to single-step
a virtual machine without landing inside interrupt handlers.

Reviewed by: jhb, corvink
Sponsored by: Google, Inc. (GSoC 2022)
Differential Revision: https://reviews.freebsd.org/D42299