arm64: correct the effect of mitigations off on kpti

If KASLR is enabled, then kpti will be forced to be enabled even if
mitigations off, so we need to adjust the description of this parameter.
Signed-off-by: Liu Song <liusong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1656033648-84181-1-git-send-email-liusong@linux.alibaba.comSigned-off-by: Will Deacon <will@kernel.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -3161,7 +3161,7 @@
 				improves system performance, but it may also
 				expose users to several CPU vulnerabilities.
 				Equivalent to: nopti [X86,PPC]
-					       kpti=0 [ARM64]
+					       if nokaslr then kpti=0 [ARM64]
 					       nospectre_v1 [X86,PPC]
 					       nobp=0 [S390]
 					       nospectre_v2 [X86,PPC,S390,ARM64]