drm/i915: Consolidate ILK_DSPCLK_GATE and PCH_DSPCLK_GATE

Register 0x42020 was defined twice under the names PCH_DSPCLK_GATE_D and
ILK_DSPCLK_GATE. This patch consolidate the 2 sets of defines in one.

The transforms done are:

PCH_DSPCLK_GATE_D    -> ILK_DSPCLK_GATE_D
ILK_DSPCLK_GATE      -> ILK_DSPCLK_GATE_D

DPARBUNIT_CLOCK_GATE_DISABLE -> ILK_DPARBUNIT_CLOCK_GATE_DISABLE
ILK_DPARB_CLK_GATE           -> ILK_DPARBUNIT_CLOCK_GATE_DISABLE

DPFDUNIT_CLOCK_GATE_DISABLE -> ILK_DPFDUNIT_CLOCK_GATE_DISABLE
ILK_DPFD_CLK_GATE           -> ILK_DPFDUNIT_CLOCK_GATE_DISABLE
ILK_CLK_FBC                 -> ILK_DPFDUNIT_CLOCK_GATE_DISABLE

DPFCRUNIT_CLOCK_GATE_DISABLE -> ILK_DPFCRUNIT_CLOCK_GATE_DISABLE
ILK_DPFC_DIS1                -> ILK_DPFCRUNIT_CLOCK_GATE_DISABLE

DPFCUNIT_CLOCK_GATE_DISABLE -> ILK_DPFCUNIT_CLOCK_GATE_DISABLE
ILK_DPFC_DIS2               -> ILK_DPFCUNIT_CLOCK_GATE_DISABLE

We have a VHRUNIT_CLOCK_GATE_DISABLE define for the pre-ILK DSPCLK_GATE_D.
Even if the same bit is used in ILK_DSPCLK_GATE_D, other bits in the
register change, so I went with re-defining it, well more precisely rename
IVB_VRHUNIT_CLK_GATE, which is not specific to IVB+. So:

IVB_VRHUNIT_CLK_GATE       -> ILK_VHRUNIT_CLOCK_GATE_DISABLE
VHRUNIT_CLOCK_GATE_DISABLE -> ILK_VHRUNIT_CLOCK_GATE_DISABLE (ILK+ code)

This commit is only a renaming commit, further commits will clean up the
logic.

v2: Rename bit 5 and 7 to _ENABLE as setting them to 1 enables clock
    gating on their respective units, contrary to all of the other bits
    (Paulo Zanoni)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>