Revert "ipq40xx: stop chromium sub-target builds on the buildbots"

This reverts commit 35d2bbc as we
believe we found that it is indeed an openssl issue, where openssl is
trying to use getrandom(2), but fails because this particular builder
has an ancient kernel without that syscall. We didn't get to the bottom
of why openssl doesn't fall back to something like /dev/random.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

target/linux/ipq40xx/chromium/target.mk

@@ -1,2 +1,2 @@
 BOARDNAME:=Google Chromium
-FEATURES += emmc boot-part rootfs-part source-only
+FEATURES += emmc boot-part rootfs-part