Samsung SoC Framebuffer driver: add Alpha Channel support

Add support for the ARGB1888 and ARGB4888 hardware to the Samsung SoC
Framebuffer driver (s3c-fb.c).

ARGB1888 and ARGB4888 is decided by var->transp.length and this variable
is set by s3c_fb_check_var().

In s3c_fb_check_var(), if var->vits_per_pixel is 25 or 28, then
var->transp.length would be 1 or 3.

Therefore alpha mode(ARGB1888 or ARGB4888) could be decided through that
variable.

For using alpha mode, you need to set the following: This code should be
added to your machine code as platform data.

static struct s3c_fb_pd_win xxx_fb_win0 = {
	/* this is to ensure we use win0 */
	.win_mode = {
		.pixclock		= (8+8+8+240)*(38+4+38+400),
		.left_margin	= 8,
		.right_margin	= 8,
		.upper_margin	= 38,
		.lower_margin	= 38,
		.hsync_len		= 8,
		.vsync_len		= 4,
		.xres			= 240,
		.yres			= 400,
	},
	.max_bpp		= 32,
	.default_bpp	= 24,
};

static struct s3c_fb_pd_win xxx_fb_win1 = {
	.win_mode = {
		.pixclock		= (8+8+8+240)*(38+4+38+400),
		.left_margin	= 8,
		.right_margin	= 8,
		.upper_margin	= 38,
		.lower_margin	= 38,
		.hsync_len		= 8,
		.vsync_len		= 4,
		.xres			= 240,
		.yres			= 400,
	},
	.max_bpp		= 32,
	.default_bpp	= 28,
};

static struct s3c_fb_platdata xxx_lcd_pdata __initdata = {
	.win[0]		= &ncp_fb_win0,
	.win[1]		= &ncp_fb_win1,
	.vidcon0	= VIDCON0_VIDOUT_RGB | VIDCON0_PNRMODE_RGB,
	.vidcon1	= VIDCON1_INV_HSYNC | VIDCON1_INV_VSYNC,
	.setup_gpio	= xxx_fb_gpio_setup,
};

s3c_fb_set_platdata(&xxx_lcd_pdata);

The above code sets pixelformat for window0 layer to RGB888 and window1
layer to ARGB4888.

Signed-off-by: InKi Dae <inki.dae@samsung.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kyungmin Park <kmpark@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>