riscv: use atomic CSR bit set/clear operations, refactor

Fix race conditions that cause broken timer interrupts.

Change-Id: I78e13a18d394b1566977e894a1def16a66c9ca5f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5883
Reviewed-by: X512 <danger_mail@list.ru>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

haiku_loader.riscv: update

* Moved machine mode code from kernel.
* Added MMU page table generation.
* Added QEMU ramfb video driver.

Change-Id: Icd67cd2e8dbf2b568d81ab8dd0d6127ca3cd97a8
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4302
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

riscv: Fix build, handle .riscv loader

* We accept the riscv loader to build it, but don't really put it
into the image since for now you'll just want the haiku_loader.riscv
for things like TinyEMU

Change-Id: I5005dd5063f2a84cf426db4c40635e87e579ad80
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4075
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: X512 <danger_mail@list.ru>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

haiku_loader: initial support for RISC-V TinyEMU

Change-Id: Ie102f466725f45072db25a9629fa8e28526484eb
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3882
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>