[PRJ][APPS] Capitalize extension of tx_initialize_low_level.s files (…

…part 1)

Extension of several tx_initialize_low_level.s files needs to be capitalized (.s --> .S) as projects' configurations refer to these files with a capitalized extension. This causes compilation errors in Linux environments.

NOTE: This first commit is necessary to ensure the extension capitalization is well considered in environments based on case-insensitive file systems.