Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

x86/ept: return correct MappingFailedLookupLevel

Prior to this change, seL4_MappingFailedLookupLevel() would retrun '22'
after any failed EPT mapping operation. This change fixes this to return
the correct amount of unresolved bits in the address.

style: set code width to 120

style: set min-conditional-indent to 0

Given we use braces all the time conditional indents do not make code
cleaner.

style: consistently attach return type

Add attach-return-type to astyle

style: consistently align pointer with name

Run astyle with align-pointer=name

x86: Rationalize names of paging structures

Changes the name of paging structure entries to more clearly indicate the kind of object
they map to. Generally this is changing a `pde_small` to `pde_pt` to indicate that this
mapping refers to a page table, removing an inconsistency where `pde_large` indicated that
the mapping was for a large page. For the same reason the `ept_pde_4k` type is changed to
`ept_pde_pt` type to reflect what is present in the actual entry.

`pde_large` is left as 'large' and not explicitly given a size as code common between
ia32 and x86-64 manipulates these entities and 'large' is already a used abstraction
over the two potential page sizes so there is need to introduce a formal abstraction layer
and make the names in the structures more specific.

Fix licenses (the rest)

s/D61/DATA61/ in license headers for consistency

[STYLE_FIX]

SELFOUR-287: 32-bit vt-x implementation

This is an implementation of vt-x for x86 kernels running in
ia32 mode.