gitignore: remove obsolete link method for arch specification
The cross_arch and cross_compile links method is obsolete and not
available any more, so we remove it from the .gitignore.
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>