Update relevant "msr {s,c}prs, reg" instructions

Updates relevant "msr {s,c}prs, reg" instructions to
"msr {s,c}prs_fsxc, reg" to avoid loosing bits when
setting SPSR/CPSR.

Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
plat-vexpress: Set CPSR.A when initializing

Sets CPSR.A when initializing a core. The bit should already be
set by the OP-TEE Dispatcher in ARM Trusted Firmware but in case
it isn't make sure the bit is set.

Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
Tested-by: Pascal Brand <pascal.brand@linaro.org> (STM platform)
Tested-by: Jens Wiklander <jens.wiklander@linaro.org> (FVP platform)
Fix wrong parameter in GCM authentication

Signed-off-by: Pascal Brand <pascal.brand@st.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Tested-by: Pascal Brand <pascal.brand@linaro.org> (STM platform)
Add stable commit to the setup FVP script

Instead of checking out latest on all Gits we have now identified a
couple of commits for all Gits (except optee_os) that could be
considered as stable commit.

Also added a script that cleans all Gits.

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>