lib: Fix log2_ceil() for 0xffffffff

Current log2_ceil(x) is defined as log2(x * 2 - 1). When x is larger
than (1 << 31), (x * 2 - 1) won't fit in u32, leading to incorrect
result. Therefore, correct it as (log2(x - 1) + 1). Also add unit tests
for inline functions in lib.h.

BUG=none
TEST=make tests/lib/lib-test
BRANCH=none

Change-Id: If868f793b909a6ad7fc48a7affac15e2c714fa2e
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59834
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

tests/lib/Makefile.inc

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+tests-y += lib-test
 tests-y += string-test
 tests-y += b64_decode-test
 tests-y += hexstrtobin-test
@@ -40,6 +41,8 @@ tests-y += cbfs-lookup-no-mcache-test
 tests-y += cbfs-lookup-has-mcache-test
 tests-y += lzma-test
 
+lib-test-srcs += tests/lib/lib-test.c
+
 string-test-srcs += tests/lib/string-test.c
 string-test-srcs += src/lib/string.c