bitmap: Fix some bugs on 32-bit platforms

bitmap: Fix some bugs on 32-bit platforms

The bitmap_word type is an unsigned long.  However in some places we assign
it using -1ULL, a 64-bit value on many platforms.  We sometimes get away
with this because it masks correctly, but in other cases it breaks things.

To clean this up define a new BITMAP_WORD_1 constant, indicating a
bitmap_word with all bits set, and use that instead of explicit UL or ULL
qualifiers.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>