target/s390x: introduce internal.h

cpu.h should only contain what really has to be accessed outside of
target/s390x/. Add internal.h which can only be used inside target/s390x/.

Move everything that isn't fast enough to run away and restructure it
right away. We'll move all kvm_* stuff later.

Minor style fixes to avoid checkpatch warning to:
- struct Lowcore: "{" goes into same line as typedef
- struct LowCore: add spaces around "-" in array length calculations
- time2tod() and tod2time(): move "{" to separate line
- get_per_atmid(): add space between ")" and "?". Move cases by one char.
- get_per_atmid(): drop extra paremthesis around (1 << 6)

Change license of new file to GPL2+ and keep copyright notice.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170818114353.13455-15-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>