boot: let BOOTSTAGE_RECORD_COUNT default to 50

boot: let BOOTSTAGE_RECORD_COUNT default to 50

BOOTSTAGE_RECORD_COUNT=30 is too small to record booting a FIT image
with EFI kernel, initrd, dtb as seen on the StarFive VisionFive 2
board.

Increase the default for BOOTSTAGE_RECORD_COUNT to 50.

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>