globally use session-qualified imports; add Lib session

Session-qualified imports will be required for Isabelle2018 and help clarify
the structure of sessions in the build tree.

This commit mainly adds a new set of sessions for lib/, including a Lib
session that includes most theories in lib/ and a few separate sessions for
parts that have dependencies beyond CParser or are separate AFP sessions.
The group "lib" collects all lib/ sessions.

As a consequence, other theories should use lib/ theories by session name,
not by path, which in turns means spec and proof sessions should also refer
to each other by session name, not path, to avoid duplicate theory errors in
theory merges later.

aspec: message_info_to_data is mostly arch independent

Factored out msg_label_bits, which is the only architecture specific part.

x64: CR3 and machine op updates for Meltdown

x64: more abstract specs and invariants for ASIDs

x64 abstract/machine: introduce and use FPUNullState

The FPU state is opaque, and its null state is not necessary an array of zeroes.
Instead, the null state is a snapshot taken after initialisation.

aspec/haskell/machine: refactor user_context interface

- remove separate abstract set_/get_register implementation, directly use machine op
- make interface aware that user_context does not always need to equal
(register => machine_word)
- introduce FPU state on x64

x64: remove all trailing whitespace

x64: Retype_R checking with sorry proofs

x64: change cte_level_bits, obj_bits (Endpoint; Notification) to 5
rather than 4.

This is true on all 64-bit platforms as the size of these objects is 4
words (4*8 = 32 = 2^5). However, this breaks the 32-bit ARM proofs that
rely on these values being 4 - see jira issue VER-725.

x64: fix ArchArch_AI

Also includes some corrections to the abstract specification, and minor
improvements to some existing proofs.

x64: fix X64 after merge, up to ArchVSpace_AI

fix ARM build after merge

Also:
- move some ARM-specific things out of Tcb_AI
- port changes from ARM to X64, up to beginning of ArchVSpace_AI

x64: updated ASpec for WordSetup arch-split

x64 invs: up to vs_refs_pages

x64: add arch_split'd x64 spec with IOMMU stuff