memlayout.h: define variables as extern

I personally dislike "common" variables, as they hid bugs a few times
for me. Thus, ppsi has "-fno-common" by now.  This commit adds
extern to memlayout.h and creates the variables in dev/sdb.c .
This builds whether or not -fno-common is there and has no effect
on a ptp-noposix build.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

dev/sdb.c

@@ -10,6 +10,15 @@
 #include <wrc.h>
 #include "hw/memlayout.h"
 
+unsigned char *BASE_MINIC;
+unsigned char *BASE_EP;
+unsigned char *BASE_SOFTPLL;
+unsigned char *BASE_PPS_GEN;
+unsigned char *BASE_SYSCON;
+unsigned char *BASE_UART;
+unsigned char *BASE_ONEWIRE;
+unsigned char *BASE_ETHERBONE_CFG;
+
 #define SDB_INTERCONNET 0x00
 #define SDB_DEVICE      0x01
 #define SDB_BRIDGE      0x02

include/hw/memlayout.h

@@ -3,14 +3,14 @@
 
 #define SDB_ADDRESS 0x30000
 
-unsigned char *BASE_MINIC;
-unsigned char *BASE_EP;
-unsigned char *BASE_SOFTPLL;
-unsigned char *BASE_PPS_GEN;
-unsigned char *BASE_SYSCON;
-unsigned char *BASE_UART;
-unsigned char *BASE_ONEWIRE;
-unsigned char *BASE_ETHERBONE_CFG;
+extern unsigned char *BASE_MINIC;
+extern unsigned char *BASE_EP;
+extern unsigned char *BASE_SOFTPLL;
+extern unsigned char *BASE_PPS_GEN;
+extern unsigned char *BASE_SYSCON;
+extern unsigned char *BASE_UART;
+extern unsigned char *BASE_ONEWIRE;
+extern unsigned char *BASE_ETHERBONE_CFG;
 
 #define FMC_EEPROM_ADR 0x50