ARM: dts: porter: remove enable prop from HS-USB device node

In  the final versions of the Porter board (called "PORTER_C") Renesas
decided to get rid  of the Maxim Integrated MAX3355 OTG chip and didn't
add any other provision to differ the host/gadget mode, so we'll have to
remove  no longer valid "renesas,enable-gpio" property from the HS-USB
device node.  Hopefully, the earlier revisions of the board were never
seen in the wild...

Fixes: c794f6a0 ("ARM: shmobile: porter: add HS-USB DT support")
Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>