ARM: dts: qcom: Update msm8974/apq8074 device trees

* Move SoC peripherals into an SoC container node
* Move serial enabling into board file (qcom-apq8074-dragonboard.dts)
* Move spi pinctrl into board file
* Cleanup cpu node to match binding spec, enable-method and compatible
  should be per cpu, not part of the container
* Drop interrupts property from l2-cache node as its not part of the
  binding spec
* Move timer node out of SoC container

Signed-off-by: Kumar Gala <galak@codeaurora.org>