arm64: Fix thread0.td_kstack_pages init

[brooks]

Summary

Commit 86a994d6537d7b5e1efb1019e466d86a688fd570 initialized
thread0.td_kstack_pages to KSTACK_PAGES, due to the lack of an
include of opt_kstack_pages.h it used the fallback value of 4 from
machine/param.h. This meant that increasing KSTACK_PAGES in the kernel
config resulted in a panic in _epoch_enter_preempt as the following
assertion was false during network stack setup:

        MPASS((vm_offset_t)et >= td->td_kstack &&
	    (vm_offset_t)et + sizeof(struct epoch_tracker) <=
	    td->td_kstack + td->td_kstack_pages * PAGE_SIZE);

Switch to initializing with kstack_pages following other architectures.

Sponsored by: DARPA, AFRL

[imp]

Matches what other architectures do. We set kstack_pages to KSTACK_PAGES in kern/kern_proc.c, and it properly includes opt_kstack_pages.h, as does arm64/locore.S where we reserve the space.

[markj]

This comment was removed by markj.