test: cmd: fdt: Test both string and integer arrays in 'fdt get value'

The 'fdt get value' subcommand now supports extraction of integer value
from integer arrays, add test for it, including a test for special case
unindexed integer array read, which is handled as hash and treated as a
long string instead of integer.

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