ARM: dts: msm: Disable U1 and U2 for MDM9x40

The device initiates U1/U2 transitions when an ACK is pending for a
Data Packet(DP). This causes the link to enter and exit low power before
the device sends an ACK for the DP. This behavior can cause a
transaction timeout on the host for the DP.

The workaround for this is to disable device initiated U1 and U2.
Host initiated U1 and U2 are still supported by default.

CRs-fixed: 756289
Change-Id: I4f497cc2b7e8716d18023f31d2d024c2050e337e
Signed-off-by: Devdutt Patnaik <dpatnaik@codeaurora.org>