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/bsd/Makefile.inc

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+tests-y += helpers-test
+
+helpers-test-srcs += tests/commonlib/bsd/helpers-test.c