LoongArch: Remove obsolete mentions of vcsr

LoongArch: Remove obsolete mentions of vcsr

The `vcsr` only exists in the old hardware design, it isn't used in any
shipped hardware from Loongson-3A5000 on. Both scalar FP and LSX/LASX
instructions use the `fcsr` as their control and status registers now.
For example, the RM control bit in fcsr0 is shared by FP, LSX and LASX
instructions.

Particularly, fcsr16 to fcsr31 are reserved for LSX/LASX now, access to
these registers has no visible effect if LSX/LASX is enabled, and will
cause SXD/ASXD exceptions if LSX/LASX is not enabled.

So, mentions of vcsr are obsolete in the first place (it was just used
for debugging), let's remove them.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Qi Hu <huqi@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>