Implement a leaner printf for Trusted Firmware

This patch implements a "tf_printf" which supports only the commonly
used format specifiers in Trusted Firmware, which uses a lot less
stack space than the stdlib printf function.

Fixes ARM-software/tf-issues#116

Change-Id: I7dfa1944f4c1e634b3e2d571f49afe02d109a351
Merge pull request #174 from soby-mathew:sm/lean_printf_v2

Implement a leaner printf for Trusted Firmware
Merge pull request #168 from sandrine-bailleux/sb/set-default-gic-arch

Define ARM_GIC_ARCH default value for all platforms
Merge pull request #167 from jcastillo-arm/jc/tf-issues/217

FVP: Ensure system reset wake-up results in cold boot