iommu/amd: Set iommu->int_enabled consistently when interrupts are set up

iommu/amd: Set iommu->int_enabled consistently when interrupts are set up

When I made the INTCAPXT support stop gratuitously pretending to be MSI,
I missed the fact that iommu_setup_msi() also sets the ->int_enabled
flag. I missed this in the iommu_setup_intcapxt() code path, which means
that a resume from suspend will try to allocate the IRQ domains again,
accidentally re-enabling interrupts as it does, resulting in much sadness.

Lift out the bit which sets iommu->int_enabled into the iommu_init_irq()
function which is also where it gets checked.

Link: https://lore.kernel.org/r/20210104132250.GE32151@zn.tnic/
Fixes: d1adcfbb520c ("iommu/amd: Fix IOMMU interrupt generation in X2APIC mode")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/50cd5f55be8ead0937ac315cd2f5b89364f6a9a5.camel@infradead.org
Signed-off-by: Will Deacon <will@kernel.org>