configs/rdn2cfg1: add new build options for ras

Introduce platform build options:
- CSS_SGI_FW_FIRST_SUPPORT: TFA build option to enable firmware first
  implementation on the RD-N2-Cfg1 platform.
- CSS_SGI_ERR_INJ_SUPPORT: TFA build option to enable error injection
  support on RD-N2-Cfg1 platform. Default value is set to 1 as RD-N2-Cfg1
  platform has either firmware-first or kernel-first error handling
  enabled.

Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I39a1c3e4ef3d1120a22ffe8abcfa481a9858768c