mesa: Set gl_constants::MinMapBufferAlignment
mesa: Set gl_constants::MinMapBufferAlignment

Leaving it set to zero isn't really correct since every allocation has
at least an alignment of 1 byte.  It also caused a problem in the i965
driver after I removed the MAX(64, ...) from the alignment calculation.
That's what I get for changing a patch without retesting it. :(

Signed-off-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73907
Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Cc: Lu Hua <65e3687feb795309330d60472c99556fa459512a@intel.com>

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