[kernel] Change VMA syscall addr param to inout

This change allows the `vma_map` and `vma_create_map` syscalls to map to
addresses other than the one specified, and therefore makes the address
parameter to those syscalls `inout` in order to return the mapped
address.

Also add the `exact` flag for specifying that mapping needs to be done
at the exact address given. If the mapping collides with another, the
new `j6_err_collision` error is returned.

definitions/objects/vma.def

@@ -17,13 +17,14 @@ object vma : object {
 
     method create_map [constructor cap:map] {
         param size size
-        param address address
+        param address address [inout]
         param flags uint32
     }
 
     method map [cap:map] {
         param process ref process [optional]
-        param address address
+        param address address [inout]
+        param flags uint32
     }
 
     method unmap [cap:unmap] {