xilinx: zynq: Add the missing function prototypes

xilinx: zynq: Add the missing function prototypes

Add the missing prototypes for the functions pointed by the below
sparse warnings
warning: no previous prototype for 'set_dfu_alt_info'
[-Wmissing-prototypes]
warning: no previous prototype for 'board_debug_uart_init'
[-Wmissing-prototypes]

Signed-off-by: Algapally Santosh Sagar <santoshsagar.algapally@amd.com>
Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@amd.com>
Link: https://lore.kernel.org/r/20230614090359.10809-7-ashok.reddy.soma@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>