nand: davinci: add support for timing configuration

This patch modifies the DaVinci NAND driver to use the
new AEMIF timing setup API to configure the NAND access
timings.

Earlier, AEMIF configuration was being done as a special
case for DM644x board, but now more boards emerge which have
capability to boot for other media (SPI flash, NOR flash) and
have the kernel access NAND flash. This means that kernel cannot
always  depend on the bootloader to setup the NAND.

Also, on platforms such as da850/omap-l138, the aemif input
frequency changes as cpu frequency changes; necessiating
re-calculation of timimg values as part of cpufreq transtitions.
This patch forms the basis for adding that support.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>