x86/RAS: Add syndrome support to mce_amd_inj

Add a debugfs file which holds the error syndrome (written into
MCA_SYND) of an injected error. Only write it on SMCA systems. Update
README file, while at it.

Signed-off-by: Yazen Ghannam <Yazen.Ghannam@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1467633035-32080-3-git-send-email-Yazen.Ghannam@amd.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>