ARM: hpe: gxp: add core support

ARM: hpe: gxp: add core support

The GXP is the HPE BMC SoC that is used in the majority
of current generation HPE servers. Traditionally the asic will
last multiple generations of server before being replaced.

Info about SoC:

HPE GXP is the name of the HPE Soc. This SoC is used to implement many BMC
features at HPE. It supports ARMv7 architecture based on the Cortex A9
core. It is capable of using an AXI bus to whicha memory controller is
attached. It has multiple SPI interfaces to connect boot flash and BIOS
flash. It uses a 10/100/1000 MAC for network connectivity. It has multiple
i2c engines to drive connectivity with a host infrastructure. There
currently are no public specifications but this process is being worked.

Signed-off-by: Nick Hawkins <nick.hawkins@hpe.com>