The following commit will introduce a variable define to remove the
duplication in the different [supe]*imximg rules.

Prepare for this by rearranging the command line flags to line up with
the letters in the extension (i.e. -e -s for esimximg instead of -s -e)
and by splitting off a multi-target rule into two.

The former improves readability when the define is introduced, as it is
then easy to see the correspondence between extension and arguments.

The latter is needed because we will call the variable for each target.

No functional change.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>