PCI: keystone: Assume controller is already in RC mode

PCI: keystone: Assume controller is already in RC mode

Keystone PCI hardware supports both RC and EP modes and devcfg register has
bits to boot strap the device to either of these modes.  It seems proper to
add this functionality to the boot loader rather than in the driver as
device will be operating in either mode, not both any time.  Currently the
driver supports only RC mode and hence register configuration in the driver
is not needed and the driver can assume the hardware is in RC mode.

Also update the DT documentation accordingly.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>