Fixes for bigendian platforms

Fixes for bigendian platforms

arch/alpha/vtophys.cc:
    PGOFSET -> ALPHA_PGOFSET to avoid include file problems
base/callback.hh:
    Added  a class to create a callback from a function
base/intmath.hh:
    make FloorLog2 inlined
dev/pcidev.cc:
    more work in getting pciconfig space happy with different endiannesses
dev/uart.cc:
    used an incorrect size for write uint64_t instead of uint8_t
sim/system.cc:
    when writing things into system data structures we need to pay
    attention to endianness

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extra : convert_revision : 52f441b5789c45db30ef2f6fd4975cbc7323a381