Convert CONFIG_SYS_BOOTM_LEN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_BOOTM_LEN

As part of this, rework error handling in boot/bootm.c so that we pass
the buffer size to handle_decomp_error as CONFIG_SYS_BOOTM_LEN will not
be available to host tools but we do know the size that we passed to
malloc().

Cc: Soeren Moch <smoch@web.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index bb956e3..d5f8421 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -335,6 +335,16 @@
 	help
 	  Support booting VxWorks images via the bootm command.
 
+config SYS_BOOTM_LEN
+	hex "Maximum size of a decompresed OS image"
+	depends on CMD_BOOTM || CMD_BOOTI || CMD_BOOTZ
+	default 0x4000000 if PPC || ARM64
+	default 0x1000000 if X86 || ARCH_MX6 || ARCH_MX7
+	default 0x800000
+	help
+	  This is the maximum size of the buffer that is used to decompress the OS
+	  image in to, if passing a compressed image to bootm/booti/bootz.
+
 config CMD_BOOTEFI
 	bool "bootefi"
 	depends on EFI_LOADER