riscv: enable DEBUG_FORCE_FUNCTION_ALIGN_64B

riscv: enable DEBUG_FORCE_FUNCTION_ALIGN_64B

Allow to force all function address 64B aligned as it is possible for
other architectures. This may be useful when verify if performance
bump is caused by function alignment changes.

Before commit 1bf18da62106 ("lib/Kconfig.debug: add ARCH dependency
for FUNCTION_ALIGN option"), riscv supports enabling the
DEBUG_FORCE_FUNCTION_ALIGN_64B option, but after that commit, each
arch needs to claim the support explicitly.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230727160356.3874-1-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>