M263: Fix redundant call to UART IRQ handler
M263: Fix redundant call to UART IRQ handler

Honor RxIrq/TxIrq to avoid redundant call to UART IRQ handler.

This is also to fix FPGA CI test mbed_hal_fpga_ci_test_shield-uart.

kjbracey-arm/mbed,mbedmicro/mbed,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,kjbracey-arm/mbed