arm64/ras: modify the error selection logic while handling ras error

Number of error records supported depends on the reset value of
ERRIDR_EL1.
There can be multiple error records supported and selction of a
particular error record is done through ERRSELR_EL1. It may be the case
that 0th index error is not supported but index 1th error is supported
on a particular platform.
While RAS error is reported and traversing through error selections, the
looping condition is based on number of records, but inside loop the
selction index needs to be incremented with each iteration. This patch
brings that change in error handling function.

Another change is just to return when handling Correctable or Deferred
error in interrupt context rather than enabling pre-emption.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Change-Id: I1ad2abe87b11acceba69493adbf946b48876bf62