riscv: select ARCH_PROC_KCORE_TEXT

This adds a separate segment for kernel text in /proc/kcore, which has a
different address than the direct linear map.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Link: https://lore.kernel.org/r/mvmh6m758ao.fsf@suse.de


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