drivers: serial: pl011: Add support for Ambiq UART

UART controller present in Ambiq SoCs is mostly compatible with PL011, but
requires some quirks that are implemented in this commit:
- the peripheral needs to be powered on first, via the PWRCTRL core,
- peripheral clock needs to be enabled and configured via the CLKEN/CLKSEL.
  registers.

The quirks mechanism was inspired by support for STM32F4 SoC in the
usb_dc_dw driver (fce0b85e).

Co-authored-by: Mateusz Sierszulski <msierszulski@antmicro.com>
Signed-off-by: Maciej Sobkowski <msobkowski@antmicro.com>
Signed-off-by: Mateusz Sierszulski <msierszulski@antmicro.com>