qemu: validate: Move disk address validation code

qemu: validate: Move disk address validation code

Move the code from 'qemuValidateDomainDeviceDefDiskFrontend' into
'qemuValidateDomainDeviceDefAddressDrive' which is called from
'qemuValidateDomainDeviceDefAddress' so that we have all address
validation code together.

This also allows us to remove the inline validation inside
'qemuBuildSCSIHostdevDevStr'.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>