PCIe:change the method to get the address of a requested capability in configuration...

PCIe:change the method to get the address of a requested capability in configuration space.

Previously, the address of a requested capability is define like that
	"#define PCI_DCR	0x78"
But, the addresses of capabilities is different with regard to PCIe revs.
So this method is not flexible.

Now a function to get the address of a requested capability is added and used.
It can get the address dynamically by capability ID.
The step of this function:
	1. Read Status register in PCIe configuration space to confirm that
	   Capabilities List is valid.
	2. Find the address of Capabilities Pointer Register.
	3. Find the address of requested capability from the first capability.

Signed-off-by: Zhao Qiang <B45475@freescale.com>