[4.15 & 4.14 stable 12/12] x86/microcode: Fix CPU synchronization routine

From: Borislav Petkov commit bb8c13d61a629276a162c1d2b1a20a815cbcfbb7 upstream Emanuel reported an issue with a hang during microcode update because my dumb idea to use one atomic synchronization variable for both rendezvous - before and after update - was simply bollocks:

[4.15 & 4.14 stable 12/12] x86/microcode: Fix CPU synchronization routine

From: Borislav Petkov commit bb8c13d61a629276a162c1d2b1a20a815cbcfbb7 upstream Emanuel reported an issue with a hang during microcode update because my dumb idea to use one atomic synchronization variable for both rendezvous - before and after update - was simply bollocks: microcode: