drm/amd/display: Allow building DC with clang on RISC-V

clang on RISC-V appears to be unaffected by the bug causing excessive
stack usage in calculate_bandwidth(). clang 16 with -fstack-usage
reports a 304 byte stack frame size with CONFIG_ARCH_RV32I, and 512
bytes with CONFIG_ARCH_RV64I.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>