video: s3c-fb: Add support EXYNOS4 FIMD

This patch adds struct s3c_fb_driverdata s3c_fb_data_exynos4 for EXYNOS4
and adds lcd clock gating support.

FIMD driver needs two clocks for FIMD IP and LCD pixel clock. Previously,
both clocks are provided by using bus clock such as HCLK. However, EXYNOS4
can not select HCLK for LCD pixel clock because the EXYNOS4 FIMD IP does not
have the CLKSEL bit of VIDCON0. So, FIMD driver should provide the lcd clock
using SCLK_FIMD as LCD pixel clock for EXYNOS4.

The driver selects enabling lcd clock according to has_clksel which means
the CLKSEL bit of VIDCON0. If there is has_clksel, the driver will not
enable the lcd clock using SCLK_FIMD because bus clock using HCLK is used
a LCD pixel clock.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>