drivers: edac: Use polling based ECC if there is no ECC IRQ

The current implementation of the LLCC's ECC mechanism
relies on an IRQ number being defined for ECC. When this
number is not available, there will not be any attempt to
see if ECC is necessary, which is not desirable.

Instead, if the ECC IRQ number is not available, default to
polling based ECC to ensure that LLCC ECC errors do not go
by unnoticed. Also, remove the EDAC_POLL_LLCC config,
as it is no longer necessary.

Change-Id: I003442400f4f42dcbfb1eaf4c57fe95449017e2a
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>