Fixes#3581.
Pins were marked as never_reset by common_hal_displayio_fourwire_construct() and common_hal_sharpdisplay_framebuffer_construct(), but these marks were never removed, so at the end of a session after displayio.release_displays(), {spi|i2c}_singleton would be set to NULL but the pins would not be reset. In the next session, board.SPI() and board.I2C() were unable to reconstruct the object because the pins were still in use.
For symmetry with creation of the singleton, add deinitialization before setting it to NULL in reset_board_busses(). This makes the pins resettable, so that reset_port(), moved behind it, then resets them.
f4f80e07ca