[nrf fromlist] drivers: serial: nrfx_uarte: Add runtime PM

Add runtime PM to the driver. When asynchronous or interrupt
driven API is used, there are 3 independent paths for enabling
the device: RX, TX and TX poll_out. TX poll_out requires special
handling because number of poll_out calls does not need to much
number of TXSTOPPED interrupts. To handle that special flag is
added. For standard RX and TX is simpler.

Upstream PR: zephyrproject-rtos/zephyr#75462

Signed-off-by: Krzysztof Chruściński <[email protected]>

Author: nordic-krch

drivers/serial/Kconfig.nrfx_uart_instance

@@ -68,6 +68,7 @@ config UART_$(nrfx_uart_num)_NRF_ASYNC_LOW_POWER
 	depends on HAS_HW_NRF_UARTE$(nrfx_uart_num)
 	depends on UART_ASYNC_API
 	depends on UART_NRFX_UARTE_LEGACY_SHIM
+	depends on !PM_DEVICE
 	default y
 	help
 	  When enabled, UARTE is enabled before each TX or RX usage and disabled