PCI: keystone: Remove duplicate MAX_*_IRQS defs

MAX_MSI_HOST_IRQS and MAX_LEGACY_HOST_IRQS are defined in both
pci-keystone.h (which is included by pci-keystone.c) and in pci-keystone.c
itself.

Remove the duplicate definitions from pci-keystone.c.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Murali Karicheri <m-karicheri2@ti.com>