ARM: OMAP2+: hwmod: rt address space index for DT

Address space is being removed from hwmod database and DT information
in <reg> property is being used. Currently the 0th index of device
address space is used to map for register target address. This is not
always true, eg. cpgmac has it's sysconfig in second address space.

Handle it by specifying index of device address space to be used for
register target. As default value of this field would be zero with
static initialization, existing behaviour of using first address space
for register target while using DT would be kept as such.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Tested-by: Mugunthan V N <mugunthanvnm@ti.com>
[paul@pwsan.com: use u8 rather than int to save memory]
Signed-off-by: Paul Walmsley <paul@pwsan.com>