uarts: 32/64 cleanup

We had lots of casts that caused warnings when compiling on RISCV.
Clean them up.

Change-Id: I46fcb33147ad6bf75e49ebfdfa05990e8c7ae4eb
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/7066
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/cpu/allwinner/a10/uart_console.c

@@ -12,7 +12,7 @@
 
 #include "memmap.h"
 
-unsigned int uart_platform_base(int idx)
+uintptr_t uart_platform_base(int idx)
 {
 	/* UART blocks are mapped 0x400 bytes apart */
 	if (idx < 8)