MLK-25349-1 dt-bindings: imx6q-pcie: add one regulator used to power up pcie phy

MLK-25349-1 dt-bindings: imx6q-pcie: add one regulator used to power up pcie phy

Both 1.8v and 3.3v power supplies can be used by i.MX8MQ PCIe PHY.
In default, the PCIE_VPH voltage is suggested to be 1.8v refer to data
sheet. When PCIE_VPH is supplied by 3.3v in the HW schematic design,
the VREG_BYPASS bits of GPR registers should be cleared from default
value 1b'1 to 1b'0. Thus, the internal 3v3 to 1v8 translator would be
turned on.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Jun Li <jun.li@nxp.com>
(cherry picked from commit c14681471c737280d93d1e5f83221576caf352ee)