qemu: support ARMv7/Cortex-A15 ...

Define Qemu AArch32 implementation for some platform functions
(core position, secondary boot cores, crash console). These are
derived from the AArch64 implementation.

BL31 on Qemu is needed only for ARMv8 and later. On ARMv7, BL32 is
the first executable image after BL2.

Support SP_MIN and OP-TEE as BL32: create a sp_min make script target
in Qemu, define mapping for IMAGE_BL32

Minor fix Qemu return value type for plat_get_ns_image_entrypoint().

Qemu model for the Cortex-A15 does not support the virtualization
extension although the core expects it. To overcome the issue, Qemu
ARMv7 configuration set ARCH_SUPPORTS_VIRTUALIZATION to 0.

Add missing AArch32 assembly macro arm_print_gic_regs from ARM platform
used by the Qemu platform.

Qemu Cortex-A15 model integrates a single cluster with up to 4 cores.

Change-Id: I65b44399071d6f5aa40d5183be11422b9ee9ca15
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>