test: cmd: fdt: Test fdt apply

test: cmd: fdt: Test fdt apply

Add 'fdt chosen' test which works as follows:
- Create basic DT, map it to sysmem
- Apply DTO which adds single property via fragment (without address spec)
- Apply DTO which adds more properties (string, u32, empty) and a subnode,
  with phandle via frament@0 and thus tests /__symbols__ node
- Apply DTO which modifies property of the previous DTO via phandle and thus
  tests the /__fixups__ node
- Print modified DT, verify it contains updates from DTOs

The test case can be triggered using:
"
./u-boot -Dc 'ut fdt'
"
To dump the full output from commands used during test, add '-v' flag.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>