riscv: Rename SiFive CLINT to RISC-V ALINT

As the RISC-V ACLINT specification is defined to be backward compatible
with the SiFive CLINT specification, we rename SiFive CLINT to RISC-V
ALINT in the source tree to be future-proof.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Rick Chen <rick@andestech.com>