siemens: board: clean up products folders vs common

The common folder was initialially created for the common parts of the
products based on draco-am355x board family. These are the product lines
'pxm2', 'rut' and the base line named 'draco'!

Adding the new capricorn-imx8 board family, common was enhanced without
cleanup.
- rename 'common/board.c' to 'common/board_am335x.c'
- add 'common/board_am335x.h' for export to the product lines

Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Signed-off-by: Enrico Leto <enrico.leto@siemens.com>
diff --git a/board/siemens/rut/board.c b/board/siemens/rut/board.c
index d9e84db..1e0e131 100644
--- a/board/siemens/rut/board.c
+++ b/board/siemens/rut/board.c
@@ -35,7 +35,7 @@
 #include <video.h>
 #include <watchdog.h>
 #include <linux/delay.h>
-#include "board.h"
+#include "../common/board_am335x.h"
 #include "../common/eeprom.h"
 #include "../common/factoryset.h"
 
@@ -43,12 +43,12 @@
 /*
  * Read header information from EEPROM into global structure.
  */
-static int read_eeprom(void)
+int draco_read_eeprom(void)
 {
 	return 0;
 }
 
-static void board_init_ddr(void)
+void draco_init_ddr(void)
 {
 struct emif_regs rut_ddr3_emif_reg_data = {
 	.sdram_config = 0x61C04AB2,
@@ -125,7 +125,7 @@
 #define REQUEST_AND_PULSE_RESET(N) \
 		request_and_pulse_reset(N, #N);
 
-static void spl_siemens_board_init(void)
+void spl_draco_board_init(void)
 {
 	REQUEST_AND_PULSE_RESET(ETH_PHY_RESET_GPIO);
 	REQUEST_AND_PULSE_RESET(MAXTOUCH_RESET_GPIO);
@@ -245,5 +245,3 @@
 	return 0;
 }
 #endif
-
-#include "../common/board.c"