pixman: replace pixman_0.24.0.bb with smaller bbappend with only diff against oe-core version

* disable iwmmxt for now, because it breaks build
* neon is not really enabled for people not having FEED_ARCH in OVERRIDES
* maybe this diff should be merged to oe-core recipes instead

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>