[ARM] 4819/1: RealView: Fix entry-macro.S to work with multiple platforms

This patch modifies the get_irqnr_preamble macro to work with multiple
platforms at run-time by reading the address of the GIC controller from
the gic_cpu_base_addr variable. This variable is defined in core.c and
intialised in realview_eb.c (gic_init_irq).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>