dt: bindings: move SEC node under new crypto/

Since technically it's not powerpc arch-specific.  Also rename it sec2
to differentiate it from its incompatible successor, the SEC 4.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

Documentation/devicetree/bindings/powerpc/fsl/sec.txt → Documentation/devicetree/bindings/crypto/fsl-sec2.txt

-Freescale SoC SEC Security Engines
+Freescale SoC SEC Security Engines versions 2.x-3.x
 
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