vboot: keep const and non-const signature and key accessors

Keep const (default) and non-const (_mutable suffix) versions
of `data` field accessors for vb2_signature and vb2_packed_key.

No need for separate 2packed_key.c file -- just static inline
the functions.

vb2_verify_packed_key_inside should return type vb2_error_t.

BUG=b:124141368, chromium:968464
TEST=make clean && make runtests
BRANCH=none

Change-Id: I96722a746f26abbb6e19a365ce74f0bfda0da381
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1786386
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
12 files changed