[Ozone-DRM] Use CRTC's mode when configuring it for mirror mode

Using the same mode on both CRTCs may not work if the timings are not
correct. This patch configures the CRTC independently such that each one
uses its own mode and timings.

Also split modesetting from re-enabling so it is easier to reason when
the CRTC's current mode can be reused.

BUG=chrome-os-partner:42915

Review URL: https://codereview.chromium.org/1338843002

Cr-Commit-Position: refs/heads/master@{#348613}
(cherry picked from commit e342544e82671b42b94e1f2f6400ddb0a5c3b49a)

Review URL: https://codereview.chromium.org/1343813002 .

Cr-Commit-Position: refs/branch-heads/2454@{#471}
Cr-Branched-From: 12bfc3360892ec53cd00fc239a47e5298beb063b-refs/heads/master@{#338390}

• ui/ozone/platform/drm/gpu/drm_vsync_provider.cc[diff]
• ui/ozone/platform/drm/gpu/hardware_display_controller.cc[diff]
• ui/ozone/platform/drm/gpu/hardware_display_controller.h[diff]
• ui/ozone/platform/drm/gpu/screen_manager.cc[diff]
• ui/ozone/platform/drm/gpu/screen_manager.h[diff]
• ui/ozone/platform/drm/gpu/screen_manager_unittest.cc[diff]