efi: Move common EFI stub code from x86 arch code to common location

No code changes made, just moving functions and #define from x86 arch
directory to common location.  Code is shared using #include, similar
to how decompression code is shared among architectures.
Signed-off-by: Roy Franz <roy.franz@linaro.org>
Acked-by: Mark Salter <msalter@redhat.com>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

arch/x86/boot/compressed/eboot.h

@@ -10,7 +10,6 @@
 #define SEG_GRANULARITY_4KB	(1 << 0)
 
 #define DESC_TYPE_CODE_DATA	(1 << 0)
-#define EFI_READ_CHUNK_SIZE	(1024 * 1024)
 
 #define EFI_CONSOLE_OUT_DEVICE_GUID    \
 	EFI_GUID(0xd3b36f2c, 0xd551, 0x11d4, 0x9a, 0x46, 0x0, 0x90, 0x27, \