Implements support for the following 128-bit atomic operations with +rcpc3:
- store-release volatile
- load-acquire volatile
- load-acquire const
- load-acquire const volatile
D126250 and D137590 added support for emitting LDAPR (Load-Acquire RCPc) rather
than LDAP (Load-Acquire) when +rcpc is available. This patch allows emitting
the 128-bit RCPc instructions added in FEAT_LRCPC3 LDIAPP/STILP. The
implementation is different from LDAPR, because there are no non-RCPc
equivalents for these new instructions.
Support for the offset variants will be added in a later patch.