ARM: dts: imx7s: Do not claim i.MX51 compatibility for SRC

ARM: dts: imx7s: Do not claim i.MX51 compatibility for SRC

System Reset Controller in i.MX7 doesn't have any commonality with IP
block found in i.MX5 and i.MX6 SoC families. Given that and the new
upstream driver for i.MX7 variant (see
https://lkml.org/lkml/2017/2/21/466) remove "fsl,imx51-src" from
compatibility string.

Cc: yurovsky@gmail.com
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: devicetree@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>