mips: spl: Flush cache before jumping to U-Boot proper

mips: spl: Flush cache before jumping to U-Boot proper

This patch adds a MIPS specific jump_to_image_no_args() implementation,
which flushes the U-Boot proper image loaded from the boot device in
SPL before jumping to it.

It has been noticed on MT76x8, that this cache flush is needed. Other
MIPS platforms might need it as well.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Weijie Gao <weijie.gao@mediatek.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>