fix(BLE): Re-implement UART with DMA on MAX32690

[crsz20]

Description

Initializing a UART peripheral with MXC_UART_IBRO_CLK would cause the MAX32690 to occasionally fail to assert a half-empty interrupt signal. This is a hardware issue.

In practice, this causes the Tx buffer to get stuck and eventually overflows. This is evident in the BLE examples with a large amount of serial output.

Solution

This device's pal_uart.c in Cordio has been re-implemented with DMA to rely on other interrupt signals to handle buffer management more reliably.

Remarks

Eric added a PAL_UART example to help test echoing in the serial output.

[crsz20]

/clang-format-run