board: freescale: p1_p2_rdb_pc: Allow to compile it without env support

When env support is disabled then usage of env_init() or env_relocate()
generates linker errors. So do not compile env_init() or env_relocate()
in SPL code when env support is disabled in SPL.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>