LoongArch: Fix probing of the CRC32 feature

Not all LoongArch processors support CRC32 instructions. This feature
is indicated by CPUCFG1.CRC32 (Bit25) but it is wrongly defined in the
previous versions of the ISA manual (and so does in loongarch.h). The
CRC32 feature is set unconditionally now, so fix it.

BTW, expose the CRC32 feature in /proc/cpuinfo.

Cc: stable@vger.kernel.org
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>