arm64: silicon-errata.rst: Sort the Cortex-A55 entries

arm64: silicon-errata.rst: Sort the Cortex-A55 entries

The Arm silicon errata list is mostly sorted by CPU name with the
exception of Cortex-A55, so let's sort it before adding more entries.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200429191921.32484-1-robh@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>