drm/i915/icl: Add macros for MMIO of DSI transcoder registers

This patch adds _MMIO_DSI macros for accessing DSI
transcoder registers.

v2: Use _MMIO_TRANS() (Ville)

Credits-to: Jani N

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/3ab94184357d63f2f87b90ef6f5029fb19bef73a.1539613303.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -9769,6 +9769,10 @@ enum skl_power_gate {
 #define _MIPI_PORT(port, a, c)	(((port) == PORT_A) ? a : c)	/* ports A and C only */
 #define _MMIO_MIPI(port, a, c)	_MMIO(_MIPI_PORT(port, a, c))
 
+/* Gen11 DSI */
+#define _MMIO_DSI(tc, dsi0, dsi1)	_MMIO_TRANS((tc) - TRANSCODER_DSI_0, \
+						    dsi0, dsi1)
+
 #define MIPIO_TXESC_CLK_DIV1			_MMIO(0x160004)
 #define  GLK_TX_ESC_CLK_DIV1_MASK			0x3FF
 #define MIPIO_TXESC_CLK_DIV2			_MMIO(0x160008)