Call devmap_bootstrap in RISC-V machine dependent code to actually create

the static device mappings.

While RISC-V support was added to subr_devmap.c in r298631, it was never
actually initialised in the machine dependent code.

Submitted by:	Nicholas O'Brien <nickisobrien_gmail.com>
Reviewed by:	br, kp
Sponsored by:	Axiado
Differential Revision:	https://reviews.freebsd.org/D21975

sys/riscv/riscv/machdep.c

@@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/bus.h>
 #include <sys/cons.h>
 #include <sys/cpu.h>
+#include <sys/devmap.h>
 #include <sys/exec.h>
 #include <sys/imgact.h>
 #include <sys/kdb.h>
@@ -898,6 +899,9 @@ initriscv(struct riscv_bootparams *rvbp)
 	kernlen = (lastaddr - KERNBASE);
 	pmap_bootstrap(rvbp->kern_l1pt, mem_regions[0].mr_start, kernlen);
 
+	/* Establish static device mappings */
+	devmap_bootstrap(0, NULL);
+
 	cninit();
 
 	init_proc0(rvbp->kern_stack);