ARM64: dts: meson-gxl: improve support for the P212 reference design

The Amlogic P212 reference design is used by other devices as well, such
as (for example) the Khadas VIM boards. Thus this patch adds and moves
all common entries from meson-gxl-s905x-p212.dts to a new, separate
meson-gxl-s905x-p212.dtsi (which can be re-used on boards such as the
Khadas VIM).
Support for all boards based on the P212 reference design includes:
- enabling IR support
- enabling the SAR ADC (SARADC_CH1 is connected to a resistor which
  indicates the hardware revision, a similar design is found on the
  Khadas VIM boards)
- all MMC controllers (which means that SDIO wifi, the SD card and the
  eMMC are now supported)
- pwm_ef as dependency for the SDIO wifi modules
- uart_A which is connected to the bluetooth module (the bluetooth
  module itself is not enabled yet due to missing devicetree bindings
  for the Broadcom serial bluetooth devices)
- uart_AO is moved to the .dtsi (as all known devices use it as their
  boot-console)

Specific to the P212 board:
- this also enables the CVBS connector (which is not available on the
  Khadas VIM boards for example)
- Realtek based SDIO wifi (instead of Broadcom which most other devices
  use)

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>