Add Kconfig IDT_IN_EVERY_STAGE to optionally specify having
the interrupt handling code available to all stages. In order
to do this the idt setup is moved to a C module. The vecX
entries are made global so that a table of references to all
the interrupt vector entry points can be used to dynamically
initialize the idt. The ramification for ramstage is that
exceptions are initialized later (lib/hardwaremain.c). Not
all stages initialize exceptions when this Kconfig variable
is selected, but bootblock for the C, stages using
assembly_entry.S, and of course ramstage do. Anything left
out just needs a call to exception_init() at the right
location.

BUG=b:72728953

Change-Id: I4146a040e5e43bed7ccc6cb0a7dc2271f1e7b7fa
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/25761


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>