riscv: Remove unused headers

Change-Id: I4cd03e043e1bc2795b98d6ec2f88efa5b50d872b
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34141
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/arch/riscv/stages.c

@@ -24,8 +24,6 @@
  * linker script.
  */
 
-#include <arch/boot.h>
-#include <arch/encoding.h>
 #include <arch/stages.h>
 #include <arch/smp/smp.h>
 #include <rules.h>