rust: irq: add flags module

rust: irq: add flags module

Manipulating IRQ flags (i.e.: IRQF_*) will soon be necessary, specially to
register IRQ handlers through bindings::request_irq().

Add a kernel::irq::Flags for that purpose.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Joel Fernandes <joelagnelf@nvidia.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250811-topics-tyr-request_irq2-v9-2-0485dcd9bcbf@collabora.com
[ Use expect(dead_code) for into_inner(), fix broken intra-doc link and
  typo. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>