Summary
The naming standard at https://cwiki.apache.org/confluence/display/NUTTX/Naming+FAQ requires that all MCU-private files begin with the name of the architecture, not up_.
This PR addresses only these name changes for the up_*.S files.
The entire job required to be compatible with that Naming Convention will also require changing the naming of the up_() functions that are used only within arch/arm and board/arm.
Impact
There should be not impact of this change (other that one step toward more consistent naming).
Testing
stm32f4discovery:netnsh
