OMAP: Add VRAM manager

Add a Video RAM manager for OMAP 2 and 3 platforms. VRAM manager is used
to allocate large continuous blocks of SDRAM or SRAM. The features VRAM
manager has that are missing from dma_alloc_* functions are:

- Support for OMAP2's SRAM
- Allocate without ioremapping
- Allocate at defined physical addresses
- Allows larger VRAM area and larger allocations

The upcoming DSS2 uses VRAM manager.

VRAM area size can be defined in kernel config, board file or with
kernel boot parameters. Board file definition overrides kernel config,
and boot parameter overrides kernel config and board file.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>