qts-filter.sh: strip DOS line endings and handle continuation lines

Some Altera Quartus generated files have long lines that are split with a '\' at
the end of the line. It also wOn Windows, rites files in DOS format, which can
confuse some of the processing scripts in this file. This patch solves both issues.

Signed-off-by: Bill Randle <bill.randle@gmail.com>
Cc: Marek Vasut <marex@denx.de>