riscv64/mmu: use struct bitfield for flags and std::atomic

Fixes some PTE concurrent access bugs.

Change-Id: I09ec56861fae389a8a3e228b17a3921b85202c8b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6949
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

mmu/riscv64: implement global page mapping support

ASID allocation is not supported yet, so always use ASID 0 for user pages for now.

Change-Id: I021e77dae692c22984bc625dd0588362bece45b7
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6698
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

riscv64/smp: Implement multi-processor support

* Working under qemu smp 1,2+
* Working on SiFive Unmatched
* x86_64 efi not broken by smp_boot_other_cpus change

Change-Id: I32ebc17913e46ed082be9ade8f56448bbf12f16e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4705
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

kernel/arch/vm: implement for riscv64

Change-Id: I0b463f3d2bca9f31b0aabacbf70a9774493d3467
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4051
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>