riscv: Drop a duplicated PAGE_KERNEL_EXEC

commit b91540d5 ("RISC-V: Add EFI runtime services") add
a duplicated PAGE_KERNEL_EXEC, kill it.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Fixes: b91540d5 ("RISC-V: Add EFI runtime services")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>