drm/i915/gt: Drop duplicate register definition for VDBOX_CGCTL3F18

Due to some mistaken merge conflict resolution, we wound up with a copy
of VDBOX_CGCTL3F18 in both intel_engine_regs.h and intel_gt_regs.h.
Since this is a per-engine register, referenced relative to an engine's
base offset, drop the copy from intel_gt_regs.h
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209051140.1599643-2-matthew.d.roper@intel.com

drivers/gpu/drm/i915/gt/intel_gt_regs.h

@@ -368,9 +368,6 @@
 #define NOPID		_MMIO(0x2094)
 #define HWSTAM		_MMIO(0x2098)
 
-#define VDBOX_CGCTL3F18(base)		_MMIO((base) + 0x3f18)
-#define   ALNUNIT_CLKGATE_DIS		REG_BIT(13)
-
 #define ERROR_GEN6	_MMIO(0x40a0)
 
 #define GEN8_FAULT_TLB_DATA0		_MMIO(0x4b10)