ewaol-config/fvp-base: Add support for runfvp

With this patch kas allows to use FVP emulator prebuilt package with runfvp
and user can run EWAOL image tests with 'kas shell' call.

To use FVP prebuilt, user has to:
 (*) set absolute path to FVP tarball in 'FVP_BASE_A_AEM_TARBALL_URI'
 (*) accept EULA, by setting 'FVP_BASE_A_ARM_EULA_ACCEPT' to "True"

This patch also updates documentaion with examples of
building and running the tests with Fvp-base.

Issue-Id: SCM-2587
Change-Id: I3b67c788fcfa110e7fa9931672d93d1c1da18172
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Signed-off-by: Kamil Dziezyk <kamil.dziezyk@arm.com>