drm/i915/icl: Allocate DSI encoder/connector

This patch allocates memory for DSI encoder and connector
which will be used for various DSI encoder/connector operations
and attaching the same to DRM subsystem. This patch also extracts
DSI modes info from VBT and save the desired mode info to connector.

v2 by Jani:
 - Drop GEN11 prefix from encoder name
 - Drop extra parenthesis
 - Drop extra local variable
 - Squash encoder power domain here

v3 by Jani:
 - Squash connector and connector helper functions here
 - Move intel_dsi_vbt_init call here

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0197023b92ffa2d59064e30fd4ca22b6a4cff16c.1543500286.git.jani.nikula@intel.com