mesa: Don't use memcpy() in _mesa_texstore() for float depth texture data

because float depth texture data needs clamping to [0.0, 1.0]. Let the
_mesa_texstore() fallback to slower path.

Fixes Khronos GLES3 CTS tests:
shadow_execution_vert
shadow_execution_frag

V2: Move the check to _mesa_texstore_can_use_memcpy() function.
    Add check for floating point data types.

Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>