remoteproc/davinci: Switch to platform_get_resource_byname()

The davinci remoteproc driver currently uses the platform_get_resource()
API for retrieving the IOMEM resources. Switch this function to use the
platform_get_resource_byname() API instead in preparation for adding the
DT support so that the binding can be agnostic of the IOMEM resource
order.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>