ata: Fix dependency for CONFIG_SATA_SIL

sata_sil.c is PCI driver and without CONFIG_PCI is building of U-Boot failing:

      LD      u-boot
    ld.bfd: drivers/ata/sata_sil.o: in function `sil_exec_cmd':
    drivers/ata/sata_sil.c:148: undefined reference to `dm_pci_phys_to_bus'
    ld.bfd: drivers/ata/sata_sil.o: in function `sil_pci_probe':
    drivers/ata/sata_sil.c:687: undefined reference to `dm_pci_get_bdf'
    ld.bfd: drivers/ata/sata_sil.c:691: undefined reference to `dm_pci_read_config16'
    ld.bfd: drivers/ata/sata_sil.c:701: undefined reference to `dm_pci_map_bar'
    ld.bfd: drivers/ata/sata_sil.c:704: undefined reference to `dm_pci_map_bar'
    ld.bfd: drivers/ata/sata_sil.c:713: undefined reference to `dm_pci_write_config16'
    ld.bfd: drivers/ata/sata_sil.c:717: undefined reference to `dm_pci_read_config16'
    ld.bfd: drivers/ata/sata_sil.o: in function `sil_cmd_identify_device':
    drivers/ata/sata_sil.c:256: undefined reference to `dm_pci_phys_to_bus'
    ld.bfd: drivers/ata/sata_sil.o: in function `sil_sata_rw_cmd':
    drivers/ata/sata_sil.c:330: undefined reference to `dm_pci_phys_to_bus'
    ld.bfd: drivers/ata/sata_sil.o: in function `sil_sata_rw_cmd_ext':
    drivers/ata/sata_sil.c:377: undefined reference to `dm_pci_phys_to_bus'
    make: *** [Makefile:1778: u-boot] Error 1

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>