davinci: support different UART bases for zImage uncompress

The davinci pre-kernel boot code assumes that all platforms use the
same UART base address for the console.  That assumption is not longer
valid with some newer SoCs so determine the console UART base address
from the machine number passed in from bootloader.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>