Intel IXP4xx OF-based physical memory map handling

configname: CONFIG_MTD_PHYSMAP_IXP4XX

Linux Kernel Configuration
└─>Device Drivers
└─>Memory Technology Device (MTD) support
└─>Mapping drivers for chip access
└─>Intel IXP4xx OF-based physical memory map handling
In linux kernel since version 5.1 (release Date: 2019-05-05)  
This provides some extra DT physmap parsing for the Intel IXP4xx
platforms, some elaborate endianness handling in particular.