Revert "RISC-V: mm: Document mmap changes"

This mmap behavior caused unintended breakages so the behavior has been
changed.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240826-riscv_mmap-v1-1-cd8962afe47f@rivosinc.com


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