arch: arm: cortex_r: linker.ld: Clean-up

This commit cleans up the linker.ld file for the Cortex-R arch.

* Convert all TAB characters to SPACE.
* Fix insane placement of curly brackets.
* Fix overall text alignments.
* Remove the special handlings for the Cortex-M devices that were
  copied from `include/arm/aarch32/cortex_m/scripts/linker.ld`.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>