cmake: Bump minimum version to 3.2.

This build error occurs with cmake 2.8.12.
/bin/sh: BYPRODUCTS: command not found

BYPRODUCTS is not available until cmake 3.2.
https://cmake.org/cmake/help/v3.2/release/3.2.html

Fixes: 2f02cf0d4c2d ("Generate xml for builtin profiles")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106370
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>