efi/arm64: add EFI_KIMG_ALIGN

The EFI stub is intimately coupled with the kernel, and takes advantage
of this by relocating the kernel at a weaker alignment than the
documented boot protocol mandates.

However, it does so by assuming it can align the kernel to the segment
alignment, and assumes that this is 64K. In subsequent patches, we'll
have to consider other details to determine this de-facto alignment
constraint.

This patch adds a new EFI_KIMG_ALIGN definition that will track the
kernel's de-facto alignment requirements. Subsequent patches will modify
this as required.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>

drivers/firmware/efi/libstub/arm64-stub.c

@@ -11,6 +11,7 @@
  */
 #include <linux/efi.h>
 #include <asm/efi.h>
+#include <asm/memory.h>
 #include <asm/sections.h>
 #include <asm/sysreg.h>
 
@@ -81,9 +82,10 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table_arg,
 		/*
 		 * If CONFIG_DEBUG_ALIGN_RODATA is not set, produce a
 		 * displacement in the interval [0, MIN_KIMG_ALIGN) that
-		 * is a multiple of the minimal segment alignment (SZ_64K)
+		 * doesn't violate this kernel's de-facto alignment
+		 * constraints.
 		 */
-		u32 mask = (MIN_KIMG_ALIGN - 1) & ~(SZ_64K - 1);
+		u32 mask = (MIN_KIMG_ALIGN - 1) & ~(EFI_KIMG_ALIGN - 1);
 		u32 offset = !IS_ENABLED(CONFIG_DEBUG_ALIGN_RODATA) ?
 			     (phys_seed >> 32) & mask : TEXT_OFFSET;