boards: arm: Add NXP mimxrt1050_evk

Adds support for the NXP MIMXRT1050-EVK board, an entry-level
development board for the new mimxrt1052 Cortex-M7 SoC.

Adds pinmuxing, dts, documentation, and jlink debug support for the new
board. Note that pinmuxing uses the mcux pinmux driver directly rather
than the Zephyr pinmux interface. The mimxrt1052 SoC has complicated
pinmuxing that may require changing the Zephyr pinmux interface to
support, so for now let's use the mcux driver directly.

We are also not yet configuring the external flash, therefore a debugger
is required to load code to the internal sram. The on-board OpenSDA
circuit with jlink firmware is sufficient, and the 'make debug' build
target is supported.

Samples tested include: hello_world, philosophers, synchronization,
basic/blinky, and basic/button.

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