arm: socfpga: soc64: Remove CONFIG_OF_EMBED

CONFIG_OF_EMBED was primarily enabled to support the S10/Agilex
spl hex file requirements.  Since this option now produces a
warning during build, and the spl hex can be created using
alternate methods, CONFIG_OF_EMBED is no longer needed.

Signed-off-by: Chee Hong Ang <chee.hong.ang@intel.com>