drm_hwcomposer: Add platformmeson for Amlogic SoC support

drm_hwcomposer: Add platformmeson for Amlogic SoC support

This specific platform handler is dedicated for the Amlogic SoC,
and more precisely for the Amlogic G12A family.

OpenGL/Mali allocation is done via a slightly modified ARM Gralloc
module, thus needing a custom platform handler to handle the custom
private_handle_t structure.

This platformmeson is based on platformhisi without the AFBC YUV
management (not handled by the Amlogic SoCs).

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Change-Id: I1a1d20b0a84b0e17aa3417c8e9633712f258523d