PCI: rcar-gen2: Drop ARM dependency from PCI_RCAR_GEN2

PCI: rcar-gen2: Drop ARM dependency from PCI_RCAR_GEN2

Since the reliance on ARM-specific struct pci_sys_data was removed, this
driver can be compile-tested on other architectures.

While at it, make the help text a bit more generic, as some members of
the R-Car Gen2 family have a different number of internal PCI
controllers.

Fixes: 4a957563fe0231e0 ("PCI: rcar-gen2: Convert to use modern host bridge probe functions")
Suggested-by: Ilpo Jarvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
[bhelgaas: add rcar-gen2 to subject]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/00f75d6732eacce93f04ffaeedc415d2db714cd6.1759480426.git.geert+renesas@glider.be