arm64: Declare non global symbols as static

arm64: Declare non global symbols as static

Fix below sparse warnings introduced while adding errata.

arch/arm64/kernel/cpu_errata.c:218:25: sparse: warning: symbol
'cavium_erratum_23154_cpus' was not declared. Should it be static?

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Linu Cherian <lcherian@marvell.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20220509043221.16361-1-lcherian@marvell.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>