kernel/arch/riscv64: restore SSTATUS register first

It cause to disable interrupts needed for correct trap frame restore.

Change-Id: I8b60023c9a878eb147796e76adb344c377cfcf11
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5255
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: X512 <danger_mail@list.ru>
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/int: implement for riscv64

Change-Id: I62d9bff75d35a685983c626720514ff17b1cef00
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4052
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>