Make mv_common.c generic for Marvell Armada38X and ArmadaXP

[mkm_semihalf.com]

Summary

Preparation for adding Armada38X and ArmadaXP SoC to GENERIC config.
Supported platform are listed in soc_family enum.
struct decode_win_spec contains platform specific functions and constants.
Function mv_check_soc_family checks SoC type and chooses proper structure during
runtime.
Platform dependent functions are splitted. Pointer to proper implementation is
chosen in runtime.
Unnecessary dummy functions are removed.
Because of changing registers name to more generic new definition of
FDT_DEVMAP_MAX in mv_machdep is added.