configs: am335x_evm: Disable ISO and EFI partitions in SPL

ISO and EFI partition configs in SPL are selected by default.
However, they are not being used.

Therefore, remove ISO and EFI partition support in SPL.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>