ARM: ep93xx: DT for the Cirrus ep93xx SoC platforms

ARM: ep93xx: DT for the Cirrus ep93xx SoC platforms

This adds compulsory device tree support to the Cirrus ep93xx ARMv4
platform.

- We select PINCTRL_EP93xx
- We select COMMON_CLK_EP93XX, as clock driver moved out of platform
  code
- We select ARCH_HAS_RESET_CONTROLLER

And also we need ARM_ATAG_DTB_COMPAT to update device tree with
information about memory passed from bootloader.

We have to leave all MACH options as they are used for board checking
before decomp, to turn off watchdog and ethernet DMA.

Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>