Allow recovery to read /proc/cmdline

avc:  denied  { read } for  pid=446 comm="recovery" name="cmdline"
dev="proc" scontext=u:r:recovery:s0
tcontext=u:object_r:proc_cmdline:s0 tclass=file

Test: build
Bug: 66497047
Change-Id: I9f48db88bed0d6ac76fa2808a4913857230a5d4b