Add support to PCIe RC controller on Intel Gateway SoCs.
PCIe controller is based of Synopsys DesignWare PCIe core.

Intel PCIe driver requires Upconfigure support, Fast Training
Sequence and link speed configurations. So adding the respective
helper functions in the PCIe DesignWare framework.
It also programs hardware autonomous speed during speed
configuration so defining it in pci_regs.h.

Also, mark Intel PCIe driver depends on MSI IRQ Domain
as Synopsys DesignWare framework depends on the
PCI_MSI_IRQ_DOMAIN.
Signed-off-by: Dilip Kota <eswara.kota@linux.intel.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>