edac: cortex_arm64_edac: Print out L2ECTLR register

The L2ECTLR register describes whether an interrupt was generated from
the L2 memory or arrived through the AXI bus.

Change-Id: Ic9416e5572743029c72f5b92b2bde978e2e7cd04
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>