riscv: Remove redundant CONFIG_64BIT from pgtable_l{4,5}_enabled

IS_ENABLED(CONFIG_64BIT) in initialization of pgtable_l{4,5}_enabled is
redundant, remove it.

Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240320064712.442579-2-dawei.li@shingroup.cn


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>