ARM: dts: msm: update PCIe PHY sigdet settings

Sigdet under low power (LP) mode will use a less accurate local reference
generation, which is expected to have a little more variation than a
precise reference (normal mode). Update PCIe PHY sigdet to use normal
mode instead of LP to increase accuracy and make sigdet more robust.

Change-Id: If9cad9ac9b5a6a736e3af653ac3b3b5e30cfefb4
Signed-off-by: Tony Truong <truong@codeaurora.org>