arm64: Make a debug print conditional on bootverbose

It doesn't seem particularly useful to have it enabled by default, and
it spits several dozen lines into the dmesg on a test system.

Reviewed by:	andrew
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D40499

sys/arm64/arm64/efirt_machdep.c

@@ -220,7 +220,10 @@ efi_create_1t1_map(struct efi_md *map, int ndesc, int descsz)
 		else
 			mode = VM_MEMATTR_DEVICE;
 
-		printf("MAP %lx mode %x pages %lu\n", p->md_phys, mode, p->md_pages);
+		if (bootverbose) {
+			printf("MAP %lx mode %x pages %lu\n",
+			    p->md_phys, mode, p->md_pages);
+		}
 
 		l3_attr = ATTR_DEFAULT | ATTR_S1_IDX(mode) |
 		    ATTR_S1_AP(ATTR_S1_AP_RW) | ATTR_S1_nG | L3_PAGE;