kernel: add missing kernel config symbol

Bump to 5.10.26 reversed dependencies on IOMMU for CONFIG_VFIO thus
malta (at least) prompted for this new symbol.

Set it to 'false' in the default config.  rockchip & X86 enable it in
target specific configs.

Thanks to Tony Ambardar for falling over this one

Signed-off-by: Kevin Darbyshire-Bryant <[email protected]>

target/linux/generic/config-5.10

@@ -6709,6 +6709,7 @@ CONFIG_VDSO=y
 # CONFIG_VF610_ADC is not set
 # CONFIG_VF610_DAC is not set
 # CONFIG_VFAT_FS is not set
+# CONFIG_VFIO is not set
 # CONFIG_VGASTATE is not set
 # CONFIG_VGA_ARB is not set
 # CONFIG_VGA_SWITCHEROO is not set