st/mesa: define ST_NEW_ flags as uint64_t values, not enums

st/mesa: define ST_NEW_ flags as uint64_t values, not enums

MSVC doesn't support 64-bit enum values, at least not with C code.
The compiler was warning:

c:\users\brian\projects\mesa\src\mesa\state_tracker\st_atom_list.h(43) : warning
 C4309: 'initializing' : truncation of constant value
c:\users\brian\projects\mesa\src\mesa\state_tracker\st_atom_list.h(44) : warning
 C4309: 'initializing' : truncation of constant value
...

And at runtime we crashed since the high 32-bits of the 'dirty' bitmask
was always 0xffffffff and the 32+u_bit_scan() index went out of bounds of
the atoms[] array.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>