ARM: tegra: allow pinmux mux option not to be set by init tables

ARM: tegra: allow pinmux mux option not to be set by init tables

Define enum PMUX_FUNC_DEFAULT, which indicates that a table entry passed
to pinmux_config_pingrp()/pinmux_config_pingrp_table() shouldn't change
the mux option in HW.

For pins that will be used as GPIOs, the mux option is irrelevant, so we
simply don't want to define any mux option in the pinmux initialization
table.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>