Add bge(4) support for big-endian architectures(part 2/2).

• removed unused funtion bge_handle_events().
• removed bus_dmamap_destroy(9) calls for DMA maps created by bus_dmamem_alloc(9). This should fix panics seen on sparc64 in device detach.
• added check for parent DMA tag creation.
• switched to use __NO_STRICT_ALIGNMENT as bge(4) supports all architectures.
• added missing bus_dmamap_sync(9) in bge_txeof().
• added missing bus_dmamap_sync(9) in bge_encap().
• corrected memory synchronization operation on status block. As the driver just read status block that was DMAed by NIC it should use BUS_DMASYNC_POSTREAD. Likewise the driver does not need to write status block back, so remove unnecessary bus_dmamap_sync(9) calls in bge_intr().
• corrected memory synchronization operation on RX return ring. The driver only read the block so remove unnecessary bus_dmamap_sync(9) in bge_rxeof().
• force bus_dmamap_sync(9) for only modified descriptors. Blindly synching all desciptor rings would reduce performance.
• call bus_dmamap_sync(9) for DMA maps that were modified in bge_rxeof().

Reviewed by: jkim(initial version)
Tested by: glebius(i386), jkim(amd64 initial version)