client.kernel: Adding handling of ppc processors

Add some code to handle building kernel on ppc machines
(32 bit versions). Also, reorganize handling on s390
and s390x.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
client.kernel_config: Introduce feature_enabled API

Check in the given kernel config file whether a given
feature is enabled. Refactor the function modules_needed
to use it.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
client.kernel_config: Add unittests

Add simple unittests for functions inside the kernel_config
module.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
client.kernel: Add support to generate U-Boot linux images

If the kernel config has CONFIG_DEFAULT_UIMAGE enabled,
we want to build a uImage (U-Boot compatible linux image),
so set the build target accordingly.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>