fsl/qe: add bit description for SYNL register for GUMR

Add the bitmask for the two bit SYNL register according to the QUICK
Engine Reference Manual.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Cc: Zhao Qiang <qiang.zhao@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>