replacing all ifndef with pargma once

All the kernel header files now use pargma once rather than the ifndef,
as the pre-processed C files do not change while header files
are protected with pargma once. This will also solve any naming issues
caused by ifndef.

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.

Increase badge size for endpoints on 64-bit platforms

This unifies the badge size of endpoints and notifications on 64-bit platforms to a
consistent 64-bits, and also changes the libsel4 definitions to match for both.

Increase size of guards on 64-bit platforms

The maximum guard size was unnecessarily restricted to 18 bits as it is on 32-bit
platforms. This change increases it to the current maximum possible of 58 bits.
The 58-bit limitation exists due to the need to encode a guard+guardsize into a
single word for cnode invocations.

libsel4: Correct 64-bit guard size bits constant

This constant was incorrectly defined as 5 when it is actually 6 on 64-bit kernels

libsel4: Make guard and badge definitions mode specific

The definitions of guard and badge sizes is going to be changed for 64-bit platforms,
this change provides an easy way of providing different definitions