riscv: Enable ARCH_HAVE_NMI_SAFE_CMPXCHG

The implement of cmpxchg() in riscv is based on atomic primitives and
has NMI-safe features, so it can be used safely in the in_nmi context.
ftrace's ringbuffer relies on NMI-safe cmpxchg() in the NMI context.
Currently, in_nmi() is true when riscv kprobe is in trap-based mode, so
this config needs to be selected, otherwise kprobetrace will not be
available.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250711090443.1688404-1-pulehui@huaweicloud.com
[pjw@kernel.org: moved to preserve alphabetical order]
Signed-off-by: Paul Walmsley <pjw@kernel.org>

arch/riscv/Kconfig

@@ -53,6 +53,7 @@ config RISCV
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAS_UBSAN
 	select ARCH_HAS_VDSO_ARCH_DATA if GENERIC_VDSO_DATA_STORE
+	select ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select ARCH_KEEP_MEMBLOCK if ACPI
 	select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE	if 64BIT && MMU
 	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX