cfi: Fix __cfi_slowpath_diag RCU usage with cpuidle

In the Linux kernel, the following vulnerability has been resolved:

cfi: Fix __cfi_slowpath_diag RCU usage with cpuidle

RCU_NONIDLE usage during __cfi_slowpath_diag can result in an invalid

RCU state in the cpuidle code path:

WARNING: CPU: 1 PID: 0 at kernel/rcu/tree.c:613 rcu_eqs_enter+0xe4/0x138

...

Call trace:

rcu_eqs_enter+0xe4/0x138

rcu_idle_enter+0xa8/0x100

cpuidle_enter_state+0x154/0x3a8

cpuidle_enter+0x3c/0x58

do_idle.llvm.6590768638138871020+0x1f4/0x2ec

cpu_startup_entry+0x28/0x2c

secondary_start_kernel+0x1b8/0x220

__secondary_switched+0x94/0x98

Instead, call rcu_irq_enter/exit to wake up RCU only when needed and

disable interrupts for the entire CFI shadow/module check when we do.