Looks like *.pblx was accidentally dropped from ignored files list and
now my "git status" is clobbered by every *.pblx image that is being
built (that's quite a lot for imx_v7_defconfig). Re-add original rule
to prevent that.

Fixes eed8a41c5 ("gitignore: ignore pblx.simximg files")

Cc: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>