The instruction and data cache line sizes of Andes core
are 64-byte. Select SYS_CACHE_SHIFT_6 for RISCV_NDS so
the SYS_CACHELINE_SIZE is enabled with a default value.
Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com> Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>