PCI: pci-bridge-emul: Fix PCIe bit conflicts

This patch fixes two bit conflicts in the pci-bridge-emul driver:

1. Bit 3 of Device Status (19 of Device Control) is marked as both
   Write-1-to-Clear and Read-Only. It should be Write-1-to-Clear.
   The Read-Only and Reserved bitmasks are shifted by 1 bit due to this
   error.

2. Bit 12 of Slot Control is marked as both Read-Write and Reserved.
   It should be Read-Write.

Link: https://lore.kernel.org/r/20200511162117.6674-2-jonathan.derrick@intel.com


Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rob Herring <robh@kernel.org>