riscv: enable SiFive errata CIP-453 and CIP-1200 Kconfig only if CONFIG_64BIT=y

The corresponding hardware issues of CONFIG_ERRATA_SIFIVE_CIP_453 and
CONFIG_ERRATA_SIFIVE_CIP_1200 only exist in the SiFive 64bit CPU cores.
Therefore, these two errata are required only if CONFIG_64BIT=y

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Fixes: bff3ff52 ("riscv: sifive: Apply errata "cip-1200" patch")
Fixes: 800149a7

 ("riscv: sifive: Apply errata "cip-453" patch")
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>