gdsys: mpc8308: Migrate SYS_FPGA{0, 1}_{BASE, SIZE} to Kconfig

Move CONFIG_SYS_FPGA0_BASE, CONFIG_SYS_FPGA0_SIZE, CONFIG_SYS_FPGA1_BASE, and
CONFIG_SYS_FPGA1_SIZE to Kconfig.

Signed-off-by: Mario Six <mario.six@gdsys.cc>