Philippe Gerum authored Jan 31, 2021 and Jan Kiszka committed Feb 03, 2021

Implement an abstract API for the low-level context switching code,
moving the legacy open coded support to the I-pipe specific section
(e.g. fpu management, register file switching, root context tracking).
Dovetail provides built-in support for all these nitty-gritty details,
which we may tap into for the same purpose instead.

The changes have been introduced in a way which properly maps to the
Dovetail interface, while remaining compatible with the interface to
the legacy code.

No functional change is introduced.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
[Jan: make giveup_fpu static]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>