qemu-io: Fix warnings from static code analysis

qemu-io: Fix warnings from static code analysis

Smatch complains about several global symbols which should be local.

Add the missing 'static' attributes and move the 'extern' declaration
of variable qemuio_misalign to qemu-io.h. This variable also changes
the type from 'int' to 'bool' which better fits documents its use.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>