x86: Break Makefile.x86 into common and pc specific ones

Now the cpu/x86/ provides a Makefile.x86_common and a
Makefile.x86_pc. The former includes the common Makefile
and adds legacy pc specific implementations (currently,
drivers only) into the building context, while the latter
has everything that defines the bootstrap of a x86 CPU.

This commit also fixes platform/galileo/ so it includes the
correct makefile - Makefile.x86_quarkX1000. Galileo uses
a Quark X1000 SoC which is not an IBM Generic PC-like CPU,
but it does provide most of a PCs peripherals through
its "Legacy Bridge". Thus, it makes sense that QuarkX1000's
Makefile includes code from the legacy_pc x86 cpu.

cpu/x86/Makefile.x86_common

@@ -1,14 +1,14 @@
-CONTIKI_CPU_DIRS = . drivers/legacy_pc
+CONTIKI_CPU_DIRS += .
 
-CONTIKI_SOURCEFILES += gdt.c helpers.S idt.c cpu.c rtc.c pit.c pic.c
+CONTIKI_SOURCEFILES += gdt.c helpers.S idt.c cpu.c
 
-### Compiler definitions
 CC       = gcc
 LD       = gcc
 AS       = as
 OBJCOPY  = objcopy
 SIZE     = size
 STRIP    = strip
+
 CFLAGSNO = -Wall -g -I/usr/local/include
 CFLAGS  += $(CFLAGSNO)
 ifeq ($(HOST_OS),Linux)

cpu/x86/Makefile.x86_quarkX1000

@@ -0,0 +1,5 @@
+include $(CONTIKI)/cpu/x86/Makefile.x86_common
+
+CONTIKI_CPU_DIRS += drivers/legacy_pc
+
+CONTIKI_SOURCEFILES += rtc.c pit.c pic.c

platform/galileo/Makefile.galileo

@@ -8,7 +8,7 @@ CONTIKI_SOURCEFILES += contiki-main.c newlib-syscalls.c loader.S clock.c rtimer-
 LINKERSCRIPT = $(CONTIKI)/platform/galileo/galileo.ld
 
 CONTIKI_CPU=$(CONTIKI)/cpu/x86
-include $(CONTIKI)/cpu/x86/Makefile.x86
+include $(CONTIKI)/cpu/x86/Makefile.x86_quarkX1000
 
 CFLAGS += -m32 -march=i586 -nostdinc -isystem $(LIBC)/include -isystem $(LIBGCC_PATH)/include -isystem $(LIBGCC_PATH)/include-fixed
 LDFLAGS += -m32 -nostdlib -T $(LINKERSCRIPT)