Uart InputClockHz hardcoded to 25 Mhz

[jpiltone]

InputClockHz for uart seems to be hardcoded before setting proper configuration for baudrate in e.g.:

https://github.com/Xilinx/embeddedsw/blob/master/lib/bsp/standalone/src/arm/cortexa53/32bit/uart.c#L94

[jpiltone]

The same issue is found in:

lib/bsp/standalone/src/cortexa53/32bit/uart.c:InputClk = 25000000U;
lib/bsp/standalone/src/cortexa53/64bit/uart.c:InputClk = 25000000U;
lib/bsp/standalone/src/cortexr5/uart.c:InputClk = 25000000U;