dma-mapping: fix ia64 build, use PHYS_PFN

kbuild test robot reports:

   In file included from include/linux/skbuff.h:34:0,
                    from include/linux/tcp.h:21,
                    from drivers/net/ethernet/amd/xgbe/xgbe-drv.c:119:
   include/linux/dma-mapping.h: In function 'dma_map_resource':
>> include/linux/dma-mapping.h:274:22: error: implicit declaration of function '__phys_to_pfn' [-Werror=implicit-function-declaration]
     unsigned long pfn = __phys_to_pfn(phys_addr);
                         ^~~~~~~~~~~~~

ia64 does not provide __phys_to_pfn(), use the PHYS_PFN() alias.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>