MLK-11776: pinctrl: freescale: fix default init state of conf regs

Fix default initialization of iomuxc mux and conf registers,
on parse group pad id relays on dafult init state to set the
corresponding pin_id value for a given pad, if default init
value is missing it can result in erroneous pinctrl configuration.

Signed-off-by: Adrian Alonso <aalonso@freescale.com>