ENGR00243106 imx: pcie: enable pcie msi on imx6 platforms

ENGR00243106 imx: pcie: enable pcie msi on imx6 platforms

deprieved from boundary msi support patch
add the following modifications
 * use the RC's line address 0x01FF8000 instead of one
 actual physical memory as the msi start address.
 The physical memory address is not mandatory required by the
 msi start address.

 * set PCI_MSI_FLAGS_ENABLE in RC's msi capability
 structure when the msi int is enabled.

 * the data of msg is only 16bit, set the upper 8bit
 cputype, and the msi int num to the lower 8bit.

Signed-off-by: Richard Zhu <r65037@freescale.com>