drm: amd/display: fix Kconfig help text

Fix help text: indent one tab + 2 spaces; end a sentence with a
period; and collapse short lines of text to one line.

Fixes: 23c61b45 ("drm/amd: Fix Kconfig indentation")
Fixes: 4562236b ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>