gpu: vivante: Add kernel side driver for GC860 with v4 interface

This is the GPL-ed driver v4.6.6 as released by Vivante,
adapted for the current kernel and for the Ingenic JZ4770 SoC
by Wladimir J. van der Laan <laanwj@gmail.com> and Steven J. Hill
<sjhill@realitydiluted.com>. Also includes some cleanups from Ben
Brewer <flatmush@googlemail.com> and myself.
gpu: vivante: Remove QNX support from v4 driver
gpu: vivante: Remove md5 stuff from v4 driver as it's not used
gpu: vivante: Removed OpenVG support
gpu: vivante: Fixed #include style

Don't use <this> for internal headers.
gpu: vivante: Removed unused header files
gpu: vivante: Removed Android support
gpu: vivante: Removed C++ checks
gpu: vivante: Removed _WIN32 checks
gpu: vivante: Removed support for compilers that are unlike GCC
gpu: vivante: Removed checks for old Linux kernel versions
gpu: vivante: Removed gc_hal_kernel_precomp.h

This was probably used for precompiled headers support at some point,
but that feature doesn't exist in our build.
gpu: vivante: Removed gc_hal_rename.h

The condition under which it renames is never true in our build.