Support for reading /dev/mem and /dev/crash

Trivial implementation of a live source.

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
Provide access to the detected page size

Provide a way to read the page_size field.

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
Put all function pointers into struct kdump_ops

Let's follow Linux kernel conventions and put all function pointers
into a common _ops structure. This may also allow modularizing the
design in the future.

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>