soc: fsl: guts: make fsl_guts_get_svr() static

The export of fsl_guts_get_svr() is a left-over, it's currently used
only internally and users needing SoC information should use the generic
soc_device infrastructure.

Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Acked-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>