[ARM] VIC: Update asm/hardware/vic.h with PL192 information

The original arch/arm/include/asm/hardware/vic.h was
written for the PL190 ARM VIC implementation, and as
such does not have any information about the PL192
version.

Add details about the PL192 and PL190 specific registers
and any changes between the two units.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>