dts: Rename k64f-gpio to kinetis-gpio

Multiple Kinetis SoCs have the same gpio hardware as the k64 and can use
the same mcux driver, so rename the dts to be more generic.

Also fixes some stranded references to kw41z-gpio to the new
kinetis-gpio.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>