target/image: allow for comments in IHEX files

target/image: allow for comments in IHEX files

This is not in the Intel hex file format specification but
some hex files may include comments (i.e. Altera USB-Blaster II
firmware) starting with '#'.

This patch makes image_ihex_buffer_complete_inner to skip
comment lines.

Change-Id: Id1f57d84d75da45e592f1c72b2b8c29193bc14e3
Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
Reviewed-on: http://openocd.zylin.com/1842
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>