efi_loader: Use EFI_CACHELINE_SIZE in the image loader too

We were using our EFI_CACHELINE_SIZE define only in the runtime service
code, but left the image loader to use plain CONFIG_SYS_CACHELINE_SIZE.

This patch moves EFI_CACHELINE_SIZE into efi_loader.h and converts
the image loader to use it.

Signed-off-by: Alexander Graf <agraf@suse.de>