gxbb: Workaround for PSCI_CPU_OFF ...

There seems to be a problem where SCP can't turn CPU0 off. Instead of
returning PSCI_E_DENIED or crashing make CPU0 wait in a WFE loop. This
way all CPUs have a consistent behaviour from the point of view of the
caller.

Change-Id: I5c8c266ca3b69c9e7a4f5ae70afeea5dd36a0825
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

gxbb: Implement PSCI_CPU_OFF ...

This works fine for CPU1-3, but it fails for CPU0, where it is simply
ignored and leaves CPU0 in a WFI loop.

Change-Id: I7d73683fdd894f2021d6a5bc2cce6cd03e18e633
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

gxbb: Initial port of Amlogic Meson S905 (GXBB) ...

The Amlogic Meson S905 is a SoC with a quad core Arm Cortex-A53 running
at 1.5Ghz. It also contains a Cortex-M3 used as SCP.

This port is a minimal implementation of BL31 capable of booting
mainline U-Boot and Linux:

- Partial SCPI support.
- Basic PSCI support (CPU_ON, SYSTEM_RESET, SYSTEM_OFF).
- GICv2 driver set up.
- Basic SIP services (read efuse data, enable/disable JTAG).

This port has been tested in an ODROID-C2.

Change-Id: Ia4bc82d7aca42a69d6b118b947279f82b3f6c6da
Tested-by: Amit Singh Tomar <amittomer25@gmail.com>
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>