arm/atomics: Move cpu-specific memory barriers to arch_cpu

* Now matches the rest of the architectures.

Change-Id: I6699e0c8f729923770f136f2c9599185a685336a
Reviewed-on: https://review.haiku-os.org/c/1527
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>

ARM: Fix dmb opcode 2 on ARMv6

* Typo, also fix tabs
* Sorry for the spam, this should be correct now

ARM: Break apart ARMv5 and older dsb/dmb

* Add isb just because.
* pdziepak pointed out that ARMv5 and before
had different barrier support.
* pdziepak also mentioned that dsb was too strong
for __sync_synchronize

ARM: Add ARMv6 or older __sync_synchronize built-in

* On ARMv6 or older, we do a simulated dsb.
* Move __sync_synchronize into thread.c in libroot
and use the new arch_atomic.h dsb/dmb defines.
* Gets arm @bootstrap-raw to end of bootstrap.

arm/atomic: fixup arch_atomic.h

* Remove _inline functions, since we're not using inlines
* Use compiler barrier instead of GCC builtin

arm: Rework hrev46863 to use gcc built-in

* Those calls were indeed v7+ only, and our toolchain
is v6.

arm: Add initial memory barrier functions

* These likely need reviewed by someone better
at arm assembly. (#10537)

ARM: Fix dmb opcode 2 on ARMv6

* Typo, also fix tabs
* Sorry for the spam, this should be correct now

ARM: Break apart ARMv5 and older dsb/dmb

* Add isb just because.
* pdziepak pointed out that ARMv5 and before
had different barrier support.
* pdziepak also mentioned that dsb was too strong
for __sync_synchronize

ARM: Add ARMv6 or older __sync_synchronize built-in

* On ARMv6 or older, we do a simulated dsb.
* Move __sync_synchronize into thread.c in libroot
and use the new arch_atomic.h dsb/dmb defines.
* Gets arm @bootstrap-raw to end of bootstrap.

arm/atomic: fixup arch_atomic.h

* Remove _inline functions, since we're not using inlines
* Use compiler barrier instead of GCC builtin

arm: Rework hrev46863 to use gcc built-in

* Those calls were indeed v7+ only, and our toolchain
is v6.

arm: Add initial memory barrier functions

* These likely need reviewed by someone better
at arm assembly. (#10537)