arm64: dts: imx8mm-beacon: Align pin configuration group names with schema

Device tree schema expects pin configuration groups to end with 'grp'
suffix.  This fixes dtbs_check warnings like:

  pinctrl@30330000: 'pcal6414-gpio', 'pmicirq', 'usdhc1grp100mhz', 'usdhc1grp200mhz', 'usdhc1grpgpio',
    'usdhc2grp100mhz', 'usdhc2grp200mhz', 'usdhc2grpgpio', 'usdhc3grp100mhz', 'usdhc3grp200mhz'
    do not match any of the regexes: 'grp$', 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>