arch/sh: don't bring common/env_embedded.o into the link

The linker script for SuperH brings the .ppcenv and .ppcenvr section
of common/env_embedded.o into the .text section. However, the .ppcenv
section is only ever filled in by env_embedded.o when
CONFIG_SYS_USE_PPCENV is defined, but no platforms in mainline U-Boot
use this.

In addition, common/env_embedded.o is not always built (when you use
CONFIG_ENV_IS_NOWHERE for example), which causes the following build
failure:

Fixes:

  LD      u-boot
/home/thomas/sh4aeb-linux-musl/bin/sh4aeb-linux-ld.bfd: cannot find common/env_embedded.o

We fix this by no longer adding the .ppcenv and .ppcenvr sections from
common/env_embedded.o into the .text section.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>