efi/cper: Add a cper_mem_err_status_str() to decode error description

Introduce a new helper function cper_mem_err_status_str() to decode the
error status value into a human readable string.

  [ bp: Massage. ]

Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220308144053.49090-2-xueshuai@linux.alibaba.com