drm/imagination: Implement MIPS firmware processor and MMU support

Add support for the MIPS firmware processor, used in the Series AXE GPU.
The MIPS firmware processor uses a separate MMU to the rest of the GPU, so
this patch adds support for that as well.

Changes since v8:
- Corrected license identifiers

Changes since v6:
- Fix integer overflow in VM map error path

Changes since v5:
- Use alloc_page() when allocating MIPS pagetable

Changes since v3:
- Get regs resource (removed from GPU resources commit)

Signed-off-by: Sarah Walker <sarah.walker@imgtec.com>
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Link: https://lore.kernel.org/r/a114f7b3e97cb07460c7f2842901716a9207b0c4.1700668843.git.donald.robson@imgtec.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>