sh: Enable ffunction-sections and fdata-sections
Enable these two options to let compiler eliminate unused code.
On R2Dplus, this results in considerable amount of saved space:
text data bss dec hex filename
- 266580 13196 39076 318852 4dd84 u-boot
+ 220214 12797 38745 271756 4258c u-boot
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Tom Rini <trini@konsulko.com>