oeqa/sdkext: Move test cases inside cases directory

For match with the new structure of the OEQA framework.

In the new framework Test component base directory in this case
sdk module will contain case and context implementations.

[YOCTO #10599]

(From OE-Core rev: bdb92fa4d9bd2e4a0a14e3adc62a6b9e9bf639d3)

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/sdkext/__init__.py

@@ -1,3 +0,0 @@
-# Enable other layers to have tests in the same named directory
-from pkgutil import extend_path
-__path__ = extend_path(__path__, __name__)