SP804 TIMER is not platform specific, and current code base adds
multiple defines to use this driver. Like FVP_USE_SP804_TIMER and
FVP_VE_USE_SP804_TIMER.

This patch removes platform specific build flag and adds generic
flag `USE_SP804_TIMER` to be set to 1 by platform if needed.

Change-Id: I5ab792c189885fd1b98ddd187f3a38ebdd0baba2
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

This patch adds support for Versatile express FVP (Fast models).
Versatile express is a family of platforms that are based on ARM v7.
Currently this port has only been tested on Cortex A7, although it
should work with other ARM V7 cores that support LPAE, generic timers,
VFP and hardware divide. Future patches will support other
cores like Cortex A5 that dont support features like LPAE
and hardware divide. This platform is tested on and only expected to
work on single core models.

Change-Id: I10893af65b8bb64da7b3bd851cab8231718e61dd
Signed-off-by: Usama Arif <usama.arif@arm.com>