arm/tegra: Fix mistake in Trimslice's pinmux

Pin group PTA does not support function RSVD3. However, the current
pinmux driver doesn't check this when setting RSVD functions, and ends
up writing 3 to the HW register. 3 is actually represented by function
GMI, so update the pinmux table to request that instead in order to
obtain the same register programming without requesting invalid
configurations.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>