ARM: socfpga: socrates: fix ENTRY_FUNCTION

The commit
	ARM: Make ENTRY_FUNCTION more robust
changed the behaviour of the ENTRY_FUNCTION. For the Socrates the call to
__barebox_arm_head() was not removed. Do so now otherwise the Socrates will
not be able to boot barebox.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>