sys-kernel: enable IOMMU on arm64

On Gigabyte R152-P31 arm64 servers, the Flatcar PXE images hang during the boot
process, making them unusable, while Fedora CoreOS images work.

The kernel seems to start correctly, however it invariably ends up printing
this message and hanging:

    ata1.00: qc timeout (cmd 0xec)
    ahci 000c:01:00.0: AHCI controller unavailable!
    pcieport 000c:00:01.0: AER: Uncorrected (Non-Fatal) error received: 000c:00:00.0
    ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4)
    pcieport 000c:00:01.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Requester ID)
    pcieport 000c:00:01.0:   device [1def:e101] error status/mask=00004000/00400000
    pcieport 000c:00:01.0:    [14] CmpltTO                (First)
    ahci 000c:01:00.0: AHCI controller unavailable!
    ahci 000c:01:00.0: AER: can't recover (no error_detected callback)
    pcieport 000c:00:01.0: AER: device recovery failed
    pcieport 000c:00:01.0: AER: Multiple Uncorrected (Non-Fatal) error received: 000c:00:00.0

Enabling IOMMU seems to make the problem disappear.

sys-kernel/coreos-modules/files/arm64_defconfig-5.15

@@ -13,6 +13,8 @@ CONFIG_ARCH_ZYNQMP=y
 CONFIG_ARM64_ACPI_PARKING_PROTOCOL=y
 CONFIG_ARM64_CRYPTO=y
 CONFIG_ARM64_VA_BITS_48=y
+CONFIG_ARM_SMMU=y
+CONFIG_ARM_SMMU_V3=y
 CONFIG_BCM7XXX_PHY=m
 CONFIG_BCMGENET=m
 CONFIG_CHR_DEV_SCH=m
@@ -33,7 +35,7 @@ CONFIG_FB_ARMCLCD=y
 CONFIG_GPIO_PL061=y
 CONFIG_GPIO_XGENE=y
 CONFIG_GPIO_XGENE_SB=y
-# CONFIG_IOMMU_SUPPORT is not set
+CONFIG_IOMMU_SUPPORT=y
 # CONFIG_IOSCHED_DEADLINE is not set
 CONFIG_KVM=y
 CONFIG_LEGACY_PTY_COUNT=16