cxl: Mask slice error interrupts after first occurrence

In some situations, a faulty AFU slice may create an interrupt storm of
slice errors, rendering the machine unusable. Since these interrupts are
informational only, present the interrupt once, then mask it off to
prevent it from being retriggered until the AFU is reset.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>