arch: arm: use dt and UCLASS_SYSCON to get gic lpi details

Use device tree and UCLASS_SYSCON driver to get
Generic Interrupt Controller (GIC) lpi address and
maximum GIC redistributors count.

Also update Kconfig to select REGMAP and SYSCON when
GIC_V3_ITS is enabled.

Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Reviewed-by: Simon Glass <sjg@chromium.org>