Report the amount of memory from smbios data if provided.

This should get the correct memory size even if a 32-bit image is running
on a machine with > 4GB of memory.  This can be useful is using a 32-bit
installer on a machine which will eventually run a 64-bit image.

Reviewed by:	kmoore

usr.sbin/pc-sysinstall/backend-query/sys-mem.sh

@@ -25,4 +25,8 @@
 #
 # $FreeBSD$
 
-expr $(sysctl -n hw.realmem) / 1048576
+if smbios_mem=$(kenv -q smbios.memory.enabled); then
+	expr $smbios_mem / 1024
+else
+	expr $(sysctl -n hw.realmem) / 1048576
+fi