To prevent an agent from indefinitely holding the mailbox firmware has
implemented a leaky bucket algorithm. Repeated access to the mailbox may
now incur a delay of up to 2.1 seconds. Add a retry loop that tries for
up to 2.5 seconds to acquire the mailbox.

Fixes: 2546c600 ("platform/x86: Add Intel Software Defined Silicon driver")
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20220420155622.1763633-2-david.e.box@linux.intel.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>