arm: gic: Don't assume the GIC base addresses are within 4G range.

There are systems out where the GIC registers (but not only) are
memory-mapped to addresses above the 4G range, eg. 0x80_0000_0000
to 0xFF_FFFF_FFFF. After following a flat (one to one) mapping a 32-bit
unsigned int isn't big enough for the 40-bit addresses. Change that to
uintptr_t.

Signed-off-by: Marek Bykowski <marek.bykowski@gmail.com>
Change-Id: Ida47495e9b2d6f4f93cbfc6eb2e497d449d6a208
3 files changed