kw41z: Add kw41z SoC

Adds initial support for the kw41z SoC. This is the first SoC in the
Kinetis W (wireless connectivity) series added to Zephyr. The kw41z
integrates a 2.4 GHz radio transceiver, BLE link layer hardware, and an
802.15.4 packet processor with an ARM Cortex M0+. It has 512 KB flash,
128 KB SRAM, and can run the system clock at up to 48 MHz.

This SoC currently has mcux shim drivers for lpuart (serial), gpio,
pinmux, i2c, and flash.

Jira: ZEP-1389
Change-Id: I8cff6d203867ba3ace7e05c36441dc8f3cbca8d8
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>