ARM: imx6q: add BYPASS support for PLL clocks

The imx6q clock driver currently hard-codes all PLL clocks to source
from OSC24M without BYPASS support.  The patch adds the missing lvds_in
clock which is mutually exclusive with lvds_gate, and implements BYPASS
and BYPASS_CLK_SRC selection for PLL clocks as per Figure 10-3. Primary
Clock Generation in IMX6DQRM, i.e. both BYPASS_CLK_SRC and BYPASS bits
are implemented as mux clocks, and ENABLE bit of PLL clocks is
implemented as a gate clock after BYPASS mux.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>