cactus: re-structure platform dependent files

This patch makes below changes to cactus:
- Platform dependent files are moved to spm/cactus/plat/arm/fvp
- Removes relative path dependency for cactus dts by copying it to build
  directory.
- Platform dependent macros are defined in cactus_platform_def.h like
  - Device base
  - Console UART
  - RX Base
  - Execution context count

Change-Id: I59e3c3f8640e01e46fc91bee4d8ce4255eaf9737
Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
11 files changed