esp32/machine_uart: Rename pyb to machine.
esp32/machine_uart: Rename pyb to machine.

MrSurly/micropython-esp32,SHA2017-badge/micropython-esp32,MrSurly/micropython-esp32,micropython/micropython-esp32,micropython/micropython-esp32,SHA2017-badge/micropython-esp32,MrSurly/micropython-esp32,micropython/micropython-esp32,SHA2017-badge/micropython-esp32,SHA2017-badge/micropython-esp32,MrSurly/micropython-esp32,SHA2017-badge/micropython-esp32,micropython/micropython-esp32,MrSurly/micropython-esp32,micropython/micropython-esp32