posix: eventfd: depends on polling

Have eventfd Kconfig select POLL is the code utilizes the polling
API.  We get a link error for tests/lib/fdtable/libraries.os.fdtable
when building on arm-clang without this.

Signed-off-by: Kumar Gala <[email protected]>
(cherry picked from commit f215e44)

Author: galak

lib/posix/Kconfig

@@ -112,6 +112,8 @@ config APP_LINK_WITH_POSIX_SUBSYS
 config EVENTFD
 	bool "Enable support for eventfd"
 	depends on !ARCH_POSIX
+	select POLL
+	default y if POSIX_API
 	help
 	  Enable support for event file descriptors, eventfd. An eventfd can
 	  be used as an event wait/notify mechanism together with POSIX calls