arm: mvebu: helios4: Reduce U-Boot image size

Remove unused I2C support in SPL and use simple_malloc functions to
reduce SPL image size.
Since Helios4 does not have any PCIe allocated on SerDes, remove PCI
support. MTD layer on top of SPI flash is not needed, remove it also.

Signed-off-by: Aditya Prayoga <aditya@kobol.io>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-By: Dennis Gilmore <dgilmore@redhat.com>
Reviewed-By: Dennis Gilmore <dgilmore@redhat.com>
Signed-off-by: Stefan Roese <sr@denx.de>