x86/bugs: Make Safe-RET robust against interrupt injection

In the Linux kernel, the following vulnerability has been resolved: x86/bugs: Make Safe-RET robust against interrupt injection An attacker injecting interrupts while the Safe-RET mitigation executes on machines affected by SRSO can neutralize the safe return sequence, potentially leading to data leakage through speculative execution. Fixup register state as if the Safe-RET sequence executed successfully by "emulating" it, in a manner of speaking, and avoid executing a RET instruction after returning from the interrupt.