sandbox: allow building sandbox_spl with CONFIG_DEBUG

sandbox: allow building sandbox_spl with CONFIG_DEBUG

Building sandbox_spl with CONFIG_DEBUG leads to errors due to missing
symbols:

    /usr/bin/ld: common/spl/spl_fit.o: in function `spl_fit_upload_fpga':
    common/spl/spl_fit.c:595: undefined reference to `fpga_load'
    /usr/bin/ld: test/test-main.o: in function `dm_test_post_run':
    test/test-main.c:124: undefined reference to `crc8'
    /usr/bin/ld: test/test-main.o: in function `dm_test_pre_run':
    test/test-main.c:95: undefined reference to `crc8'
    collect2: error: ld returned 1 exit status

This is due to -Og not eliminating unused functions.

Add FPGA and CRC8 support to the defconfig. Sandbox tests for
SPL_FPGA and CRC8 should be created. So enabling these setting
is advised anyway.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>