scripts: Introduce {quiet_,}cmd_bin2c

Add a make command to compile binary files as C data through bin2c with

    $(call,bin2c,<data_name_prefix>)

Note that this requires BUILD_BIN2C=y.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>