non_plat: Allow vendor_init to set mtk_dsbp_support_prop

DSBP property is set by multiple mediatek devices to declare support
for the same. It is already labeled in property_contexts but seems to
missing permission for vendor_init to actually set it.

Denial observed without this change:
[    4.713173] .(7)[1:init]selinux: avc:  denied  { set } for property=persist.vendor.radio.mtk_dsbp_support pid=1 uid=0 gid=0 scontext=u:r:vendor_init:s0 tcontext=u:object_r:mtk_dsbp_support_prop:s0 tclass=property_service permissive=1\x0a

Test: Boot and observe that propery is set without any denial

Signed-off-by: Aayush Gupta <[email protected]>
Change-Id: I0cc0c2cadbf9edb3fb205b9e52074f852fe08658