imx: imx_clock: Add driver and associated clock register definitions

imx: imx_clock: Add driver and associated clock register definitions

This commit:

- Defines a clock stub with a conjoined header defining the clock
  memory map.

- Defines the CCM Clock Gating Register which comes in a quadrumvirate
  register set to read, set, clear and toggle individual clock gates into
  one of four states based bitmask.

  00: Domain clocks not needed
  01: Domain clocks needed when in RUN
  10: Domain clocks needed when in RUN and WAIT
  11: Domain clocks needed all the time

- Defines clock control register bits

  There are various quadrumvirate register blocks target-root, misc-root,
  post-root, pre-root in the CCM.

  The number of registers is huge but the four registers in each
  quadrumvirate block contain the same bits, so the number of bit
  definitions is actually quite low.

- Defines clock identifiers

  An array of clock gates is provided in the CCM block. In order to index
  that array and thus enable/disable clock gates for the right components,
  we need to provide meaningful names to the indices.

  Section 5.2.5 of the i.MX7 Solo Application Processor Reference Manual
  Rev 0.1 provides the relevant details.

- Defines target mux select bits
  This is a comprehensive definition of the target clock mux select bits.
  These bits are required to correctly select the clock source. Defining
  all of the bits up-front even for unused blocks in ATF means we can
  switch on any block we want at a later date without having to write new
  code in the clock-mux layer.

- Defines identifier indices into root-slice array
  The root-slice array of control registers has a specific set of indices,
  which differ from the clock-gate indices.

- Provides a clock gate enable/disable routine
  Provides a clock-gate enable/disable routine via the set/clr
  registers in a given clock-gate control register block.

  This index passed should be one of the enums associated with CCM and
  depending on enable/disable being passed either set or clr will be
  written to.

  The Domain0 bits are currently the only bits targeted by this write, more
  work may need to be done on the domain bits in subsequent patches as a
  result.

- imx: Adds set/clr routines to clock layer

  Adds a set and clr routine to the clock layer. These routines allow us to
  access the set and clear registers of the "target" block registers. These
  are the registers where we select the clock source from the available list.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>