powerpc: fsl_law: Add definition for first PCIe target interface

powerpc: fsl_law: Add definition for first PCIe target interface

Header file asm/fsl_law.h already provides correct definition for second
and third PCIe controller (LAW_TRGT_IF_PCIE_2 and LAW_TRGT_IF_PCIE_3). But
is missing definition for the first PCIe controller (LAW_TRGT_IF_PCIE_1).

Note that existing definition for LAW_TRGT_IF_PCIE_2 and LAW_TRGT_IF_PCIE_3
are slightly complicated, but are really correct for P2020 platform.

Signed-off-by: Pali Rohár <pali@kernel.org>