The syscon APIs were used for selecting the state of the mux
device because the mmio-mux driver in u-boot did not support
the mux functionality when the parent device is not a syscon.
Change to mux APIs which utilizes the reg-mux driver to select the
state of the multiplexer.
Signed-off-by: Anurag Dutta <a-dutta@ti.com>
(cherry picked from commit a42b8b0b3f)