drm/i915: add support for mPHY destination on intel_sbi_{read, write}

This way we should be able to write mPHY registers using the Sideband
Interface in the next commit. Also fixed some syntax oddities in the
related code.

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

drivers/gpu/drm/i915/i915_drv.h

@@ -382,6 +382,11 @@ enum intel_pch {
 	PCH_LPT,	/* Lynxpoint PCH */
 };
 
+enum intel_sbi_destination {
+	SBI_ICLK,
+	SBI_MPHY,
+};
+
 #define QUIRK_PIPEA_FORCE (1<<0)
 #define QUIRK_LVDS_SSC_DISABLE (1<<1)
 #define QUIRK_INVERT_BRIGHTNESS (1<<2)