RISCV: get RISCV to build again

This makes lzmadecode 64-bit clean (I hope).
It also cleans up a few other nits.

Change-Id: I24492e9f357e8d3a6de6abc351267f900eb4a19a
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/7623
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/mainboard/emulation/qemu-riscv/uart.c

@@ -21,7 +21,6 @@
 #include <console/uart.h>
 #include <arch/io.h>
 #include <boot/coreboot_tables.h>
-#include "frontend.h"
 
 static uint8_t *buf = (void *)0x3f8;
 uintptr_t uart_platform_base(int idx)