MIPS: ingenic: Initial JZ4770 support

MIPS: ingenic: Initial JZ4770 support

Provide just enough bits (clocks, clocksource, uart) to allow a kernel
to boot on the JZ4770 SoC to a initramfs userspace.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Reviewed-by: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Maarten ter Huurne <maarten@treewalker.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18487/
Signed-off-by: James Hogan <jhogan@kernel.org>