MAINTAINERS: update EXYNOS DP DRIVER F: patterns

Add patterns for Exynos DP header to MAINTAINERS file.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>