Added assembly files to freertos_port_files()

[eivindbergem]

Some ports have assembly as well as C files.

[schteve]

Apologies for taking a while on this. Seems like an easy one to accept - it makes sense to include assembly (and probably other port files) in the list so the rebuild happens when changing them. Two things:

1. Could you remove the eprintln!()? I guess it's probably a debug thing left in.
2. Does it make sense to add both .s and .S files? I think the string check is case sensitive.

[eivindbergem]

1. Could you remove the `eprintln!()`? I guess it's probably a debug thing left in.

Will do.

2. Does it make sense to add both .s and .S files? I think the string check is case sensitive.

I did a search in the FreeRTOS kernel repo and there are both .s and .S. I'll add matching for both.

[schteve]

Thanks!