x86: cleanup e820_setup_gap(), v2

e820_search_gap also take a end_addr parameter to limit search from
start_addr to end_addr.

Signed-off-by: AloK N Kataria <akataria@vmware.com>
Acked-by: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: "lenb@kernel.org" <lenb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>