MIPS: ingenic: Detect machtype from SoC compatible string

Previously, the mips_machtype variable was always initialized
to MACH_INGENIC_JZ4740 even if running on different SoCs.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
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/18486/


Signed-off-by: James Hogan <jhogan@kernel.org>