[ARM] pxa: PXA_SHARPSL_DETECT_MACH_ID to include head-sharpsl.S

With kexec-based kernel boot loader on Zaurus, the machine ID is
actually correctly passed, and head-sharpsl.S is not necessary.
Introduce PXA_SHARPSL_DETECT_MACH_ID, and include head-sharpsl.S
only when that's explicitly enabled.
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>

arch/arm/boot/compressed/Makefile

@@ -36,7 +36,7 @@ ifeq ($(CONFIG_CPU_XSCALE),y)
 OBJS		+= head-xscale.o
 endif
 
-ifeq ($(CONFIG_PXA_SHARPSL),y)
+ifeq ($(CONFIG_PXA_SHARPSL_DETECT_MACH_ID),y)
 OBJS		+= head-sharpsl.o
 endif
 

arch/arm/mach-pxa/Kconfig

@@ -458,6 +458,14 @@ config PXA_SHARPSL
 	  SL-C3000 (Spitz), SL-C3100 (Borzoi) or SL-C6000x (Tosa)
 	  handheld computer.
 
+config PXA_SHARPSL_DETECT_MACH_ID
+	bool "Detect machine ID at run-time in the decompressor"
+	depends on PXA_SHARPSL
+	help
+	  Say Y here if you want the zImage decompressor to detect
+	  the Zaurus machine ID at run-time. For latest kexec-based
+	  boot loader, this is not necessary.
+
 config MACH_POODLE
 	bool "Enable Sharp SL-5600 (Poodle) Support"
 	depends on PXA_SHARPSL