package/refpolicy: move patches to subdirectory

refpolicy patches are for 2.20210908 upstream version but when using a custom
version from git they may fail to apply.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/1734417630

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>