meta: Use float for temporary images, not (un)signed normalized.

meta: Use float for temporary images, not (un)signed normalized.

In commit 091eb15b694, Jordan changed get_temp_image_type() to use
_mesa_get_format_datatype() instead of returning GL_FLOAT.  That has
several possible return values: GL_FLOAT, GL_INT, GL_UNSIGNED_INT,
GL_SIGNED_NORMALIZED, and GL_UNSIGNED_NORMALIZED.

We do want to use GL_INT/GL_UNSIGNED_INT for integer formats.  However,
we want to continue using GL_FLOAT for the normalized fixed-point types.
There isn't any code in pack.c to handle GL_(UN)SIGNED_NORMALIZED.

Fixes oglconform's fboarb advanced.blit.copypix, which was regressed by
commit 091eb15b694a396f8453093575ccec2db7f14eb8.

NOTE: This is a candidate for the 9.0 branch.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53573
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>