arm: Convert assembly files to C

Minimizing the amount of assembly we use makes it easier to understand
the early boot flow and how objects are placed in the ELF image.

Additionally, arm_init_ccr() is no longer called before the C runtime
initialization is done, and is instead called by main().

Change-Id: Ib539bd45fb707d6948cc925a024cce803051ff8a
Signed-off-by: Chris Kay <chris.kay@arm.com>