Add support for assigning memory regions dynamically to peripherals
attached to GPMC interface. Platform specific code should now call
gpmc_cs_request to get a free GPMC memory region instead of using
a fixed address.

Make the H4 and Apollon platform initialization use the new API.
Signed-off-by: Imre Deak <imre.deak@solidboot.com>
Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>