misc: rtsx: Add support for RTS5260

Add support for new chip rts5260.
In order to support rts5260, the definitions of
some internal registers and workflow have to be
modified and are different from its predecessors
and OCP function is added for RTS5260. So we need
this patch to ensure RTS5260 can work.

Signed-off-by: Rui Feng <rui_feng@realsil.com.cn>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Tested-by: Perry Yuan <perry_yuan@dell.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>