riscv: Select ARCH_SUPPORTS_ATOMIC_RMW by default

Select ARCH_SUPPORTS_ATOMIC_RMW by default to enable osqlocks.
Signed-off-by: Chenxi Mao <maochenxi@eswin.com>
[Palmer: commit text]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -13,6 +13,7 @@ config 32BIT
 config RISCV
 	def_bool y
 	select ARCH_CLOCKSOURCE_INIT
+	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_HAS_BINFMT_FLAT
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
 	select ARCH_HAS_DEBUG_WX