debian/testsuite-xfail-debian.mk: mark misc/tst-pkey as XFAIL on alpha, arm64...

debian/testsuite-xfail-debian.mk: mark misc/tst-pkey as XFAIL on alpha, arm64 and mips*, as there is a disagreement between kernel and glibc how to report missing protection key support when the syscalls have been wired.