msm: kgsl: Remove pm_qos_latency from legacy pdata struct

Remove pm_qos_latency from the legacy pdata struct and read it
directly from the device tree in kgsl_pwrctrl_init().

Change-Id: Ic0dedbad9a53c1cb357e78cf5899c70a155066c5
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>