feat(neoverse-rd): add firmware definitions for fourth gen platforms

Add firmware definitions for the fourth generation of platforms. The
following files are added -

- nrd_css_fw_def4.h	: for CSS firmware definitions
- nrd_ros_fw_def4.h 	: for RoS firmware definitions
- nrd_plat_arm_def4.h	: for platform port macros
- nrd_pas_def4.h 	: for PAS definitions

All the common files for these platforms are housed under nrd4
directory.

Signed-off-by: Joel Goddard <joel.goddard@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Signed-off-by: Lokesh B V <Lokesh.BV@Arm.com>
Change-Id: I92ca66c00216eabf2c674d3135c0652d4df7a404