x86: rename remap percpu first chunk allocator to lpage

The "remap" allocator remaps large pages to build the first chunk;
however, the name isn't very good because 4k allocator remaps too and
the whole point of the remap allocator is using large page mapping.
The allocator will be generalized and exported outside of x86, rename
it to lpage before that happens.

percpu_alloc kernel parameter is updated to accept both "remap" and
"lpage" for lpage allocator.

[ Impact: code cleanup, kernel parameter argument updated ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>