frdm_kw41z: Add frdm_kw41z board

Adds initial support and documentation for the frdm_kw41z board.

- Configures the kw41 to use the 32 MHz external oscillator on the board
  to generate a 40 MHz system clock. The clock settings match the MCUX
  SDK hello_world example project.
- Provides pinmux settings for the uart, i2c, LEDs, and switches
- Enables pinmux, gpio, uart, and i2c driver instances
- Configures the fxos8700 accelerometer/magnetometer driver

Jira: ZEP-1390
Change-Id: I025a0eae3d380eaf90b02683acf5c592e2204a2e
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>