LoongArch: Support LA32R aliases rdcnt{vl,vh,id}.w

LoongArch: Support LA32R aliases rdcnt{vl,vh,id}.w

These LA32R instructions are in fact special cases of the LA32S/LA64
rdtime{l,h}.w (with only one output operand instead of two, the other
one being forced to $zero), but are named differently in the LA32R
ISA manual nevertheless.

As the LA32R names are more memorable to a degree (especially for those
having difficulties remembering which operand corresponds to the node
ID), support them by making them aliases of the corresponding LA32S/LA64
instruction respectively, and make them render as such in disassembly.

Signed-off-by: WANG Xuerui <git@xen0n.name>