doc: update system requirements in Linux guide

doc: update system requirements in Linux guide

Update the system requirements section of the doc to cover builds with
meson and ninja. This involves updating the package dependencies to include
meson, ninja and python 3.5, and also updating the optional dependencies
section to explain that the components are enabled/disabled automatically
by meson.

As part of this update, the relevant sections were simplified to keep the
document shorter. For mandatory requirements, we can refer to the various
distro's development tools package groups rather than requiring gcc, core
tools etc. individually. The optional package list was very incomplete, and
if complete would duplicate information in the individual driver's guides.
Therefore we can simplify it by listing only the library optional
requirements and referring users to the driver docs to find details on
their dependencies.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>