drm/i915: Use a private interface for register access within GT

The GT functions for enabling register access also need to occasionally
write to and read from registers. To avoid the potential recursion as we
modify the public interface to be stricter, introduce a private register
access API for the GT functions.

v2: Rebase
v3: Rebase onto uncore
v4: Use raw interfaces consistently so that we only use the low-level
    readN functions from a single location.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -2133,22 +2133,20 @@ void intel_sbi_write(struct drm_i915_private *dev_priv, u16 reg, u32 value,
 int vlv_gpu_freq(int ddr_freq, int val);
 int vlv_freq_opcode(int ddr_freq, int val);
 
-#define __i915_read(x, y) \
+#define __i915_read(x) \
 	u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg);
-
-__i915_read(8, b)
-__i915_read(16, w)
-__i915_read(32, l)
-__i915_read(64, q)
+__i915_read(8)
+__i915_read(16)
+__i915_read(32)
+__i915_read(64)
 #undef __i915_read
 
-#define __i915_write(x, y) \
+#define __i915_write(x) \
 	void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val);
-
-__i915_write(8, b)
-__i915_write(16, w)
-__i915_write(32, l)
-__i915_write(64, q)
+__i915_write(8)
+__i915_write(16)
+__i915_write(32)
+__i915_write(64)
 #undef __i915_write
 
 #define I915_READ8(reg)		i915_read8(dev_priv, (reg))