arm64: add cmdline to control ptrauth feature at boot

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7QNYP

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Add a `arm64.nopauth=` cmdline to control kernel's perception to CPU's
hardware capability of pointer authentication at early boot stage, which
provides a method to turn off the PAuth feature without affecting kABI.

The new cmdline parameter shares the same name with the one introduced
by the commit ("arm64: cpufeatures: Allow disabling of Pointer Auth from
the command-line") in 5.12 kernel, which is implemented in a different
mechanism (check the link below).

Link: https://patchwork.kernel.org/project/linux-arm-kernel/patch/20210208095732.3267263-23-maz@kernel.org/


Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>