gdb: LoongArch: Support reg aliases in info reg command

According to LoongArch ELF ABI specification [1], support the register
aliases in "info register" command.

Without this patch:
```
(gdb) info reg a0
Invalid register `a0'

```
With this patch:

```
(gdb) info reg a0

a0             0x1                 1

```
[1] https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html#_register_convention

Signed-off-by: Hui Li <lihui@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
1 file changed