ARM: OMAP: DMA: use constant array maximum, drop some LCD DMA code

gcc can apparently handle stack-allocated arrays that use a dynamic
variable as the array maximum.  Rather than using a mutable quantity,
simply use a constant maximum possible size.  To me, code clarity is
improved; and it also avoids the following sparse warnings:

arch/arm/plat-omap/dma.c:886:40: error: bad constant expression
arch/arm/plat-omap/dma.c:892:17: error: cannot size expression
arch/arm/plat-omap/dma.c:970:40: error: bad constant expression
arch/arm/plat-omap/dma.c:972:17: error: cannot size expression

Also drop some dead code from the OMAP1 LCD DMA code:

arch/arm/mach-omap1/lcd_dma.c:80:6: warning: symbol 'omap_set_lcd_dma_src_port' was not declared. Should it be static?

Signed-off-by: Paul Walmsley <paul@pwsan.com>