classes/patch.bbclass: Create a "patches" directory when initialising

classes/patch.bbclass: Create a "patches" directory when initialising
the quilt patcher class. Without this quilt will search for a patches
directory - starting from the current directory up to the root
directory. If it finds an existing patches directory it will use it
for its patches. This causes all sorts of problems since it is not
where the patches are expected to be. Prior to the recent patcher
changes this directory was being created.