The ARMv8 RAS Extensions introduced Standard Error Records which are a
set of standard registers through which:

  - Platform can configure RAS node policy; e.g., notification
    mechanism;

  - RAS nodes can record and expose error information for error handling
    agents.

Standard Error Records can either be accessed via. memory-mapped
or System registers. This patch adds helper functions to access
registers and fields within an error record.

Change-Id: I6594ba799f4a1789d7b1e45b3e17fd40e7e0ba5c
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>