boot: change some arch ifdefs to feature ifdefs

The routines boot_ramdisk_high, boot_get_cmdline and boot_get_kbd
are currently enabled by various combinations of CONFIG_M68K,
CONFIG_POWERPC and CONFIG_SPARC.

Use CONFIG_SYS_BOOT_<FEATURE> defines instead.

CONFIG_SYS_BOOT_RAMDISK_HIGH
CONFIG_SYS_BOOT_GET_CMDLINE
CONFIG_SYS_BOOT_GET_KBD

Define these as appropriate in arch/include/asm/config.h files.

Signed-off-by: John Rigby <john.rigby@linaro.org>
Acked-by: Wolfgang Denk <wd@denx.de>
diff --git a/README b/README
index a52f3bf..a507a1f 100644
--- a/README
+++ b/README
@@ -2275,6 +2275,19 @@
 		all data for the Linux kernel must be between "bootm_low"
 		and "bootm_low" + CONFIG_SYS_BOOTMAPSZ.
 
+- CONFIG_SYS_BOOT_RAMDISK_HIGH:
+		Enable initrd_high functionality.  If defined then the
+		initrd_high feature is enabled and the bootm ramdisk subcommand
+		is enabled.
+
+- CONFIG_SYS_BOOT_GET_CMDLINE:
+		Enables allocating and saving kernel cmdline in space between
+		"bootm_low" and "bootm_low" + BOOTMAPSZ.
+
+- CONFIG_SYS_BOOT_GET_KBD:
+		Enables allocating and saving a kernel copy of the bd_info in
+		space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
+
 - CONFIG_SYS_MAX_FLASH_BANKS:
 		Max number of Flash memory banks