board: wexler: qc750: add WEXLER Tab 7t support

WEXLER Tab 7t is a mini tablet computer developed by WEXLER that
runs the Android operating system. The device features a 7.0-inch
(180 mm) HD display, an Nvidia Tegra 3 quad-core chip, 1 GB of RAM,
8, 16 or 32 GB of storage that can be supplemented with a microSDXC
card giving up to 64 GB of additional storage and a full size USB
port.

Tested-by: Maksim Kurnosenko <asusx2@mail.ru>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
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