ARM64: dts: meson-gxl-p23x: Add SD/SDIO/MMC and PWM nodes

Add SD/SDIO/MMC nodes and PWM 32768Hz clock configuration to provide
storage and WiFi functionality on the p23x boards.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>