Davinci: gpio - use ioremap()

This patch modifies the gpio_base definition in davinci_soc_info to be a
physical address, which is then ioremap()ed by the gpio initialization
function.

Signed-off-by: Cyril Chemparathy <cyril@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>