drm/panel: p079zca: Refactor panel driver to support multiple panels

Refactor Innolux P079ZCA panel driver, let it support multi panels from
Innolux that share similar power sequences.

Panels may require different power supplies so use regulator bulk
interfaces and define per panel supply-names.

Changes in v2:
- Change regulator property name to meet the panel datasheet
Changes in v3:
- this patch only refactor P079ZCA panel to support multi panel,
  support P097PFG panel in another patch
Changes in v4:
- Modify the patch which suggest by Thierry
Changes in v5:
- use regulator_bulk to handle different supply number

Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180702102721.3546-2-heiko@sntech.de