zygo: config: turn off MICROCODE_DBG (kills AP bringup under KVM on 7.3)

zygo: config: turn off MICROCODE_DBG (kills AP bringup under KVM on 7.3)

With CONFIG_MICROCODE_DBG=y the microcode loader runs under a hypervisor
(it is normally skipped there), and on 7.3-rc2 its ucode_dbg() printk on
a secondary CPU (load_ucode_amd_ap -> apply_microcode_amd -> find_patch
-> get_patch_level) reaches nbcon_kthreads_wake -> irq_work_queue ->
x2apic_send_IPI_self before the AP has enabled x2APIC: an unchecked
WRMSR to 0x83f, the AP dies and the VM resets.  Every 7.3-rc2 boot on
the bhive test VM (Ryzen 3700X guest) died at "smpboot: x86: Booting
SMP configuration:" with no further output; the same kernel boots with
maxcpus=1.  6.18 tolerates the option.  It is a debug knob and off is
the normal configuration.

Assisted-by: Claude:claude-opus-4-8