bsps: Move startup files to bsps

Adjust build support files to new directory layout.

This patch is a part of the BSP source reorganization.

Update #3285.

bsps/arm/stm32f4/start/bsp_specs

@@ -0,0 +1,9 @@
+%rename endfile old_endfile
+%rename startfile old_startfile
+
+*startfile:
+%{!qrtems: %(old_startfile)} \
+%{!nostdlib: %{qrtems: crti.o%s crtbegin.o%s}}
+
+*endfile:
+%{!qrtems: %(old_endfiles)} %{qrtems: crtend.o%s crtn.o%s}