board: gateworks: gw_ventana: use comomn GSC driver

board: gateworks: gw_ventana: use comomn GSC driver

Use the common GSC driver.

This allows us to do some additional cleanup:
 - use the GSC driver functions
 - move waiting for the EEPROM to the SPL int (it will always be ready
   after this)
 - move eeprom functions into eeprom file and elimate GSC_I2C_BUS
 - eliminate some redundant EEPROM reads (the EEPROM must be read in
   SPL before relocation, in SPL after relocation, and in U-Boot init.
   All subsequent uses can use the global structure)
 - remove unnecessary header files and alphabatize includes

Signed-off-by: Tim Harvey <tharvey@gateworks.com>