gpu: vivante: Clean up build system files.

Clean up the CFLAGS to match the newer Vivante driver code from the
'etna_viv' project. Make config options the same as 'etna_viv'.

Signed-off-by: Steven J. Hill <sjhill@realitydiluted.com>
gpu: vivante: Make kernel memory map functions generic again.

The functions 'do_mmap_pgoff' and 'do_munmap' are not exported to
driver modules. For Ingenic and other MIPS platforms, wrapper
functions are used instead.

Signed-off-by: Steven J. Hill <sjhill@realitydiluted.com>