arm64: defconfig: Enable Librem 5 devkit components

The Librem 5 devkit is based on NXP's i.MX8MQ. Schematics are at
https://source.puri.sm/Librem5/dvk-mx8m-bsb

.

This enables drivers for the following hardware components that aren't
yet enabled in defconfig:

- Goodix GT5688 touchscreen
- iMX8MQ's PWM for the LCD backlight
- TI BQ25896 charge controller
- NXP SGTL5000 audio codec
- Microcrystal RV-4162-C7 RTC
- magnetometer: CONFIG_IIO_ST_MAGN_3AXIS
- the SIMCom SIM7100E/A modem
- NXP PTN5110HQZ usb-c controller

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>