EDAC/ghes: Add a notifier for reporting memory errors

In order to make it a proper module and disentangle it from facilities,
add a notifier for reporting memory errors. Use an atomic notifier
because calls sites like ghes_proc_in_irq() run in interrupt context.

  [ bp: Massage commit message. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Jia He <justin.he@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221010023559.69655-3-justin.he@arm.com