That code was added for booting from NOR. When you boot from NOR, the boot ROM only pin muxes 12-bits of address for non-muxed NOR and 16-bits of address for muxed NOR. So some code is not available until after the pin-muxing for the rest of the GPMC address space . That pin-muxing must be done in the first 4k of address space for non-mux NOR or the first 16k of address space for muxed NOR. The assembler code is doing the pin-muxing of the rest of the address space.
Can you post any changes you made? I should be able to figure out why your board is hanging.
Steve K.