common: env_embedded: allow fine placement of environment object

common: env_embedded: allow fine placement of environment object

Commit 7653942b10e9e ("common/env_embedded.c: drop support for
CONFIG_SYS_USE_PPCENV") dropped the .ppcenv section which was
used in linking scripts to allow fine placement of embedded
environment sections.

This implies that GCC randomly places objects from env/embedded.o
and environment is not guaranteed to be located at the correct address:

04003df8 g     F .text  00000038 mii_init
04004000 g     O .text  00000004 env_size
04004004 g     O .text  00002000 environment
04006004 g     F .text  00000040 .hidden __lshrdi3

This patch restores this capability by allocating each object marked
with __UBOOT_ENV_SECTION__ into a different section. Hence
'environment' will be alone in .text.environment, allowing a
fine placement in u-boot.lds with:

		. = DEFINED(env_offset) ? env_offset : .;
		env/embedded.o			(.text.environment)

Fixes: 7653942b10e9e ("common/env_embedded.c: drop support for CONFIG_SYS_USE_PPCENV")
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>