spec: support gbs(1) incremental builds

spec: support gbs(1) incremental builds

gbs(1) enable incremental builds that are significantly faster, hoewever,
spec files need some adjustments.

+ You can't use -n <name> with %setup
+ There is no point in making mrproper
+ use rsync(1) instead of cp(1)+find(1) to copy devel files

Other changes are:
+ use make headers_install to install headers in the buildroot
+ add _smp_mflags to make(1) things faster

Change-Id: Ia14fbe7acab8b83683f9e07757b4f62a7657b2a5
Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>