envf: Support more common read env in SPL

1. Rename env_get_part_table() to envf_get(),
and make it more common use.

2. Avoid read env from flash multi times.

Change-Id: I4fb005be13babba0fdeea129b

envf: Support more common read env in SPL

1. Rename env_get_part_table() to envf_get(),
and make it more common use.

2. Avoid read env from flash multi times.

Change-Id: I4fb005be13babba0fdeea129b18f45d8f19d8730
Signed-off-by: Xuhui Lin <xuhui.lin@rock-chips.com>

show more ...