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.

ARM: Add support to flush L1 caches

Extend the existing seL4_BenchmarkFlushCaches without modifing the usage
of it. Will be used in sel4bench to measure the cold cache performance.

arm: CONFIG_L1_CACHE_LINE_SIZE_BITS in cmake

Move definition of L1_CACHE_LINE_SIZE_BITS to cmake where it is set
according to the arm processor family.

This removes duplication in the hardware.h header files and makes adding
a new processor family require less lines changed.

style: consistently attach return type

Add attach-return-type to astyle

arm: Rename plat_cleanInvalidateCache

Rename plat_cleanInvalidateCache to plat_cleanInvalidateL2Cache to
indicate that it is a L2 cache maintenance operation only.

[STYLE_FIX]

add seL4_BenchmarkFlushCaches() for arm and ia32

Available when CONFIG_ENABLE_BENCHMARKS is set, flushes caches for
running cold-cache benchmarks

Ghost assertions about max object size.

Release snapshot