kexec: Move ELF fields to struct kimage

ELF related fields elf_headers, elf_headers_sz, and elf_load_addr are
defined in architecture specific 'struct kimage_arch' for x86, powerpc,
and arm64. The name of these fields are different in these
architectures that makes it hard to have a common code for setting up
the device tree for kexec system call.

Move the ELF fields to 'struct kimage' defined in include/linux/kexec.h
so common code can use it.

Suggested-by: Rob Herring <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Lakshmi Ramasubramanian <[e-mail]>
Reviewed-by: Thiago Jung Bauermann <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

include/linux/kexec.h

···
 	/* Virtual address of IMA measurement buffer for kexec syscall */
 	void *ima_buffer;
 #endif
+
+	/* Core ELF header buffer */
+	void *elf_headers;
+	unsigned long elf_headers_sz;
+	unsigned long elf_load_addr;
 };
 
 /* kexec interface functions */