arm64: dts: qcom: sm7225: Add device tree for Fairphone 4

Add device tree for the Fairphone 4 smartphone which is based on
Snapdragon 750G (sm7225) which is basically sm6350.

Currently supported are UART, physical buttons (power & volume), screen
(based on simple-framebuffer set up by the bootloader), regulators and
USB.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211007212444.328034-12-luca@z3ntu.xyz