juno: Split platform.h into separate headers ...

Change-Id: Ic0abaa12f13a6a1dead41c914c6c103a65f273fa

juno: Implement 'plat_print_gic_regs' macro ...

The 'plat_print_gic_regs' macro will print the contents of
the GICC_IAR and GICC_CTLR registers.

Change-Id: Ib435522c2d597e15c31fe05f9b0b310b9053206c