Makefile: tweaks

- Removed hardcoded toolchain.
- -o3 & Cortex-A15 optimizations.

Signed-off-by: LaboDJ <jacopolabardi@gmail.com>

Conflicts:

	Makefile
vfp: Cortex-A15 optimizations

Signed-off-by: LaboDJ <jacopolabardi@gmail.com>
arm: Cortex-A15 optimizations

Signed-off-by: LaboDJ <jacopolabardi@gmail.com>

Conflicts:

	arch/arm/Makefile
defconfig: enable optimizations
makefile: tune flags
GPU: add optimization flags to GPU drivers

Signed-off-by: Lens-F <tnoah12@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
Compressed: optimize for Cortex A15

Signed-off-by: LaboDJ <jacopolabardi@gmail.com>