e2fsck: use real functions for kernel slab functions

e2fsck: use real functions for kernel slab functions

The macros that e2fsck uses to implement kmalloc et al. use only some of
their arguments, so unlike standard function calls, they can cause
compiler warnings like:

./../e2fsck/revoke.c:141:8: warning: variable 'gfp_mask' set but not used [-Wunused-but-set-variable]

Fix this by providing a proper definition for each function, making sure
to match the function prototypes used in the kernel.

Remove the kmem_cache_t typedef, as it doesn't exist in the kernel.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>