lib/genalloc.c: fix allocation of aligned buffer from non-aligned chunk

lib/genalloc.c: fix allocation of aligned buffer from non-aligned chunk

gen_pool_alloc_algo() uses different allocation functions implementing
different allocation algorithms.  With gen_pool_first_fit_align()
allocation function, the returned address should be aligned on the
requested boundary.

If chunk start address isn't aligned on the requested boundary, the
returned address isn't aligned too.  The only way to get properly
aligned address is to initialize the pool with chunks aligned on the
requested boundary.  If want to have an ability to allocate buffers
aligned on different boundaries (for example, 4K, 1MB, ...), the chunk
start address should be aligned on the max possible alignment.

This happens because gen_pool_first_fit_align() looks for properly
aligned memory block without taking into account the chunk start address
alignment.

To fix this, we provide chunk start address to
gen_pool_first_fit_align() and change its implementation such that it
starts looking for properly aligned block with appropriate offset
(exactly as is done in CMA).

Link: https://lkml.kernel.org/lkml/a170cf65-6884-3592-1de9-4c235888cc8a@intel.com
Link: http://lkml.kernel.org/r/1541690953-4623-1-git-send-email-alexey.skidanov@intel.com
Signed-off-by: Alexey Skidanov <alexey.skidanov@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Daniel Mentz <danielmentz@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Laura Abbott <labbott@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>