hwrng: omap3-rom - Fix missing clock by probing with device tree

[ Upstream commit 0c0ef9ea6f3f0d5979dc7b094b0a184c1a94716b ]

Commit 0ed266d7 ("clk: ti: omap3: cleanup unnecessary clock aliases")
removed old omap3 clock framework aliases but caused omap3-rom-rng to
stop working with clock not found error.

Based on discussions on the mailing list it was requested by Tero Kristo
that it would be best to fix this issue by probing omap3-rom-rng using
device tree to provide a proper clk property. The other option would be
to add back the missing clock alias, but that does not help moving things
forward with removing old legacy platform_data.

Let's also add a proper device tree binding and keep it together with
the fix.

Cc: devicetree@vger.kernel.org
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Adam Ford <aford173@gmail.com>
Cc: Pali Rohár <pali.rohar@gmail.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Tero Kristo <t-kristo@ti.com>
Fixes: 0ed266d7 ("clk: ti: omap3: cleanup unnecessary clock aliases")
Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>