Documentation: ARM: EXYNOS: Extend boot loader interface documentation

Extend the kernel-bootloader interface documentation with usage of
register INFORM1 (0x0804) and different CPU resume address on Exynos542x
family (with Multi-Cluster Power Management enabled).

Additionally add glossary and reformat section titles.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>