Revert "Revert "fs: add read_iter and write_iter to several file systems""

This reverts commit 6b9f60b99caa140063f836936c4ded1292c28fc6.
Revert "ARM: fault: assume no context when IRQs are disabled during data abort."

This reverts commit b8578f6fbb7dffb552f23fa30064c0acb90c5638.
Revert "ARM: mutex: use generic atomic_dec-based implementation for ARMv6+"

This reverts commit 00cc4703f801da5b2f5df0738a8d3fa57cc085b0.
Revert "ARM: 7467/1: mutex: use generic xchg-based implementation for ARMv6+"

This reverts commit 7d035857efa58ad11186d93b0265630ebd68b716.