fwk: Add support of OS interrupt operation

Update the interface of fwk_interrupt_global_{enable|disable} functions to
save and restore the current interrupt state.

Add a new framework interface to get current interrupt context state:
- fwk_is_interrupt_context()

No functional change expected to current arch.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Tarek El-Sherbiny <tarek.el-sherbiny@arm.com>
Change-Id: I61569d1ff21bbc7d7bcc82eee32fc6d7d28b8469