binder: do unlocked work in binder_alloc_new_buf()

binder: do unlocked work in binder_alloc_new_buf()

Extract non-critical sections from binder_alloc_new_buf_locked() that
don't require holding the alloc->mutex. While we are here, consolidate
the checks for size overflow and zero-sized padding into a separate
sanitized_size() helper function.

Also add a few touchups to follow the coding guidelines.

Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20231201172212.1813387-12-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>