risc-v/mpfs: avoid OpenSBI redefinition conflicts

This drops the dependency to riscv_internal.h which ensures
less redefinition conflicts. OpenSBI declares some of the
variables again which are spread in many NuttX files.

Signed-off-by: Eero Nurkkala <eero.nurkkala@offcode.fi>

arch/risc-v/src/mpfs/mpfs_opensbi.c

@@ -26,7 +26,6 @@
 #include <assert.h>
 #include <errno.h>
 #include <stdint.h>
-#include <riscv_internal.h>
 #include <riscv_arch.h>
 
 #include <hardware/mpfs_plic.h>
@@ -118,6 +117,16 @@ static int  mpfs_irqchip_init(bool cold_boot);
 static int  mpfs_ipi_init(bool cold_boot);
 static int  mpfs_timer_init(bool cold_boot);
 
+/****************************************************************************
+ * Extern Function Declarations
+ ****************************************************************************/
+
+/* riscv_internal.h cannot be included due to a number of redefinition
+ * conflicts.  Thus, define the riscv_lowputc() with the extern definition.
+ */
+
+extern void riscv_lowputc(char ch);
+
 /****************************************************************************
  * Private Data
  ****************************************************************************/