Staging: lustre: ptlrpc: layout: Declare as static

Declare req_capsule_init_area and req_capsule_field_present as static
since they are used only in this particular file. Also remove the
corresponding declarations from header files.

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>