helpers: Introduce retry macro

Introduce a macro retry(attempts, condition, expr) for retrying a
condition, which is extensively used in coreboot.

Example usage:

 if (!retry(3, read32(REG) == 0, mdelay(1))
         printk(BIOS_ERR, "Error waiting for REG to be 0\n");

BUG=none
TEST=make tests/commonlib/bsd/helpers-test
TEST=emerge-cherry coreboot
BRANCH=none

Change-Id: I421e4dcab949616bd68b3a14231da744b9f74eeb
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55778
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

tests/commonlib/Makefile.inc

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+subdirs-y += bsd
+
 tests-y += region-test
 
 region-test-srcs += tests/commonlib/region-test.c