Makefile: Add support for generating C array at compile time

Generating C array at compile time based on details provided by
objects.mk is a very useful feature which will help us compile
only a subset of drivers or modules.

We add a bash script (carray.sh) which takes array details and
object/variable list from command-line to generate a C source
containing array of object/variable pointers. We also extend
top-level makefile to use carray.sh whenever specified through
objects.mk.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>