dt-bindings: arm: fsl: Add Y Soft IOTA Phoenix, Lynx, Pegasus and Pegasus+

These i.MX6 boards are based on a facelifted PCB from the previous designs.
Routing for some unused parts was completely removed (uSD card, PCIe, audio
codec) and some new parts were added (supercap backed RTC, secure element,
PWM audio, GPIO button).

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Michal Vokáč <michal.vokac@ysoft.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>