drm/i915/dsi: Use a fuzzy check for burst mode clock check

Prior to this commit we fail to init the DSI panel on the GPD MicroPC:
https://www.indiegogo.com/projects/gpd-micropc-6-inch-handheld-industry-laptop#/

The problem is intel_dsi_vbt_init() failing with the following error:
*ERROR* Burst mode freq is less than computed

The pclk in the VBT panel modeline is 70000, together with 24 bpp and
4 lines this results in a bitrate value of 70000 * 24 / 4 = 420000.
But the target_burst_mode_freq in the VBT is 418000.

This commit works around this problem by adding an intel_fuzzy_clock_check
when target_burst_mode_freq < bitrate and setting target_burst_mode_freq to
bitrate when that checks succeeds, fixing the panel not working.

Cc: stable@vger.kernel.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190524174028.21659-2-hdegoede@redhat.com

drivers/gpu/drm/i915/intel_drv.h

@@ -1557,6 +1557,7 @@ int vlv_force_pll_on(struct drm_i915_private *dev_priv, enum pipe pipe,
 		     const struct dpll *dpll);
 void vlv_force_pll_off(struct drm_i915_private *dev_priv, enum pipe pipe);
 int lpt_get_iclkip(struct drm_i915_private *dev_priv);
+bool intel_fuzzy_clock_check(int clock1, int clock2);
 
 /* modesetting asserts */
 void assert_panel_unlocked(struct drm_i915_private *dev_priv,