pinctrl: imx: output one pin/config pair per line in pinconf-groups

cat /sys/kernel/debug/pinctrl/${pinctrl}/pinconf-groups output is
hardly readable, if a pin group contains more than one pin the output
is glued and looks like this:

  MX6Q_PAD_SD1_DAT0: 0x17071MX6Q_PAD_SD1_CMD: 0x17071MX6Q_PAD_SD1_CLK: 0x17071

Add two space indentation and a new line separator to improve
readability of the output.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>