ARM: dts: imx6sx: Align pin config nodes with bindings

ARM: dts: imx6sx: Align pin config nodes with bindings

Bindings expect pin configuration nodes in pinctrl to match certain
naming and not be part of another fake node:

pinctrl@30330000: '...' does not match any of the regexes: 'grp$', 'pinctrl-[0-9]+'

Drop the wrapping node and adjust the names to have "grp" prefix.
Diff looks big but this should have no functional impact, use e.g.
git show -w to view the diff.

Signed-off-by: Marek Vasut <[email protected]>
Signed-off-by: Shawn Guo <[email protected]>