riscv: Align on L1_CACHE_BYTES when STRICT_KERNEL_RWX

Allows the sections to be aligned on smaller boundaries and
therefore results in a smaller kernel image size.

Signed-off-by: Sebastien Van Cauwenberghe <svancau@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>