Remove BSS section access by 'plat_print_gic' during crash reporting

This patch avoids the problem of crash reporting mechanism accessing
global data in BSS by 'plat_print_gic_regs' for FVP platforms. Earlier
it depended on the global 'plat_config' object for the GIC Base address
in FVP platforms which would have caused exception if it were accessed
before the BSS was initialized. It is now fixed by dynamically
querying the V2M_SYS_ID to find the FVP model type and accordingly
selecting the appropriate GIC Base address.

This patch also fixes the 'plat_print_gic_regs' to use the correct GIC
Distributor base address for printing GICD_IS_PENDR register values
for both Juno and FVP platforms.

Fixes ARM-Software/tf-issues#236

Change-Id: I545c7b908b3111419bf27db0575ce86acf86784b