Keep hashed user tokens, with the following changes:
32-bit physical device addresses are mapped directly to user-tokens. No
    duplicate maps are allowed, and the addresses are assumed to be outside
    of the range 0x10000000 through 0x30000000. The user-token is identical
    to the 32-bit physical start-address of the map.
64-bit physical device addressed are mapped to user-tokens in the range
0x10000000 to 0x30000000 with page-size increments. The user_token should
    not be interpreted as an address.
Other map types, like upcoming TTM maps are mapped to user-tokens in the
    range
0x10000000 to 0x30000000 with page-size increments. The user_token should
    not be interpreted as an address.

Implement hashed map lookups.

Signed-off-by: Dave Airlie <airlied@linux.ie>