linux-yocto: fix race between checkout and meta data generation

linux-yocto: fix race between checkout and meta data generation

There are two tasks that must run before a linux-yocto kernel is built.

  - Kernel checkout and relocation to work-shared (kernel_checkout)
  - Meta data gathering and configuration prep (kernel_metadata)

The current task definitions for both are simply "before do_patch",
which is correct, but kernel_checkout must run before and not race with
kernel_metadata.

So we set the definition of kernel_checkout to be more specific and
enforce the proper ordering.

[YOCTO: #7731]

(From OE-Core rev: 9d806f3d05de918952f839f5e595cb71cd1261db)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>