arm64/cpuinfo: only show one cpu's info in c_show()

arm64/cpuinfo: only show one cpu's info in c_show()

Currently, when ARM64 displays CPU information, every call to c_show()
assembles all CPU information. However, as the number of CPUs increases,
this can lead to insufficient buffer space due to excessive assembly in
a single call, causing repeated expansion and multiple calls to c_show().

To prevent this invalid c_show() call, only one CPU's information is
assembled each time c_show() is called.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20250421062947.4072855-1-yebin@huaweicloud.com
Signed-off-by: Will Deacon <will@kernel.org>