Introduce IS_IN_ELX() macros

The goal of these macros is to improve code readability by providing
a concise way to check whether we are running in the expected
exception level.

Change-Id: If9aebadfb6299a5196e9a582b442f0971d9909b1
fvp: Provide per-EL MMU setup functions

Instead of having a single version of the MMU setup functions for all
bootloader images that can execute either in EL3 or in EL1, provide
separate functions for EL1 and EL3. Each bootloader image can then
call the appropriate version of these functions. The aim is to reduce
the amount of code compiled in each BL image by embedding only what's
needed (e.g. BL1 to embed only EL3 variants).

Change-Id: Ib86831d5450cf778ae78c9c1f7553fe91274c2fa
Fix C accessors to GIC distributor registers with set/clear semantics

This patch fixes C accessors to GIC registers that follow a set/clear
semantic to change the state of an interrupt, instead of read/write/modify.
These registers are:
  Set-Enable
  Clear-Enable
  Set-Pending
  Clear-Pending
  Set-Active
  Clear-Active
For instance, to enable an interrupt we write a one to the corresponding bit
in the Set-Enable register, whereas to disable it we write a one to the
corresponding bit in the Clear-Enable register.

Fixes ARM-software/tf-issues#137

Change-Id: I3b66bad94d0b28e0fe08c9042bac0bf5ffa07944
fvp: Use the right implem. of plat_report_exception() in BL3-2

On FVP, the file 'plat/fvp/aarch64/plat_helpers.S' contains an
FVP-specific implementation of the function 'plat_report_exception()',
which is meant to override the default implementation. However, this
file was not included into the BL3-2 image, meaning it was still
using the default implementation. This patch fixes the FVP makefile
to compile this file in.

Change-Id: I3d44b9ec3a9de7e2762e0887d3599b185d3e28d2
Merge pull request #68 from jcastillo-arm/jc/tf-issues/137

Change-Id: If8744c38c2d5c50caa7454b055e2ba418cf1e8bf
Merge pull request #69 from sandrine-bailleux:sb/split-mmu-fcts-per-el
Merge pull request #71 from sandrine-bailleux:sb/fix-tsp-fvp-makefile