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.

style: consistently attach return type

Add attach-return-type to astyle

Move some lockTLB magic into C.

This patch moves the 'outer' chunk of lockTLBEntry into C rather
than handwritten assembly. The outer chunk accesses a global
counter and does arithmetic. The inner chunk (lockTLBEntryCritical)
writes to the registers, must be specially aligned, and is generally
special.

The change reduces unnecessary handwritten assembly, and also avoids
a special case that was problematic for binary verification.