This PR adds the Frame Buffer Driver for PINE64 PinePhone. With this driver, NuttX Apps will be able to use the standard Frame Buffer API to render graphics on PinePhone.
`boards/arm64/a64/pinephone/src/pinephone_bringup.c`: Render Test Pattern after calling `up_fbinitialize()` to start the Frame Buffer Driver
`boards/arm64/a64/pinephone/src/pinephone_display.c`: Add Frame Buffer Driver
`boards/arm64/a64/pinephone/src/pinephone_display.h`: Declare new function for rendering Test Pattern
`platforms/arm/a64/boards/pinephone/index.rst`: Add Frame Buffer as supported driver for PinePhone
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