Revert "softirq: use ffs() in __do_softirq()"

This reverts commit 7ccc447cc0b18d7fa8582fa02c2da7d9c5109840.
Revert "sched: Introduce preempt_count accessor functions"

This reverts commit a2052895e7846a092c3f61b0119d58969bb41392.
Revert "irq: Optimize softirq stack selection in irq exit"

This reverts commit 0d2554ab0690b8cfac5cff4d32c8adb1612e017f.
Revert "irq: Justify the various softirq stack choices"

This reverts commit 117099dabc940a6e73d6b089497fe7dd589f5f4d.
Revert "irq: Improve a bit softirq debugging"

This reverts commit c3a8b7c8999c8aff5049f534c36af0f668df0ac3.
Revert "irq: Optimize call to softirq on hardirq exit"

This reverts commit 3b55d287e0d681908f32f5bb30c0b0dbc2566b92.
Revert "irq: Consolidate do_softirq() arch overriden implementations"

This reverts commit 7b46839e0db077fe769877f8c7daafa0a8193d7f.
Revert "irq: Force hardirq exit's softirq processing on its own stack"

This reverts commit cba9daeb738e47109ed14e603f8b96f04f566981.
Revert "Fix lockup related to stop_machine being stuck in __do_softirq."

This reverts commit 4751d5d81938a937f917d4403276e7092ff258d4.
Revert "irq: Don't re-enable interrupts at the end of irq_exit"

This reverts commit 5ae14a56ed40a66abd095d04e3f4ddd7a68dd46e.
Revert "irq: Remove IRQ_EXIT_OFFSET workaround"

This reverts commit 994e384927dee2cdffd0f9673c7f16cae720dd57.
Revert "irq: Sanitize invoke_softirq"

This reverts commit a2efa18f10e75014665a8f2b0675f13cb5b03259.
Revert "irq: Ensure irq_exit() code runs with interrupts disabled"

This reverts commit af4149fbca79b49b9ddcdb9cb42096125f20cfbb.