Documentation: edac: Add bindings for arm64 cpu erp

This is a snapshot from msm-3.18 upto the
commit 262b8c5814ec ("edac: cortex_arm64_edac:
modify sbe detection to use perf events") for the
arm64 cache cpu erp bindings.

Change-Id: I7313a121440bf5a455401cf73bd5ef4d6c1506cb
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>