ARM: dts: imx6ul: segin: Fix LED naming for phyCORE and PEB-EVAL-01

Fix node name for the user LEDs to prevent the pinctrl of the phyCORE's
leds node from being overwritten. Also use more generic names for user
LEDs.

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>