Hello Jimmy, the confusion arose due to inconsistent documentation in the i.MX53 UG manual :
25.3.3 Multiplexed Address/Data Mode
In this mode, multiplexing addresses and data bits on the same pins is supported for
synchronous/asynchronous accesses to x8/x16/ x32 data width memory devices.
For more information about the pins that drive data/address in 8/16/32 non-muxed mode
and 16/32 muxed mode, refer to the EIM Internal Module Multiplexing table in the EIM
Internal Pads Allocation chapter of the datasheet.
In fact, do as you want, x8 bits mode does not work in multiplexed mode...
Regards.