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/include/console/uart.h

@@ -45,7 +45,7 @@ void uart_tx_byte(int idx, unsigned char data);
 void uart_tx_flush(int idx);
 unsigned char uart_rx_byte(int idx);
 
-unsigned int uart_platform_base(int idx);
+uintptr_t uart_platform_base(int idx);
 
 #if !defined(__ROMCC__)
 static inline void *uart_platform_baseptr(int idx)