Align _end symbol to at least 4 in all MIPS scripts

Align _end symbol to at least 4 in all MIPS scripts

Left-over part of commit 84b2a020daa17d8ee5c9ec979c3d56f95e69573b

The _end marker must be aligned to 4-bytes to ensure that the last
element written does not reach beyond the address of _end.  This is
also necessary as the termination condition is an equality test
instead of an ordered test so (_end - _fbss) must be a multiple of
4-bytes.  The alignment is already correct for mti*.ld files, fix
it for all remaining MIPS scripts that don't already align to at
least 4.