tools: cell-linux: Use minimal decompression space for ARM64

Factor out a default decompression factor for ARM because ARM64 does not
perform any compression so far, thus has a factor of 1 only. This allows
for more compact non-root Linux cell layout during load.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>

tools/jailhouse-cell-linux

@@ -310,8 +310,10 @@ class ARMCommon:
         if args.initrd:
             ramdisk_size = page_align(os.fstat(args.initrd.fileno()).st_size)
             # leave sufficient space between the kernel and the initrd
-            image_size += kernel_size * 4
-            kernel_size *= 5
+            decompression_factor = self.default_decompression_factor()
+            decompression_space = decompression_factor * kernel_size
+            kernel_size += decompression_space
+            image_size += decompression_space
 
         if not args.dtb:
             print('No device tree specified', file=sys.stderr)
@@ -425,6 +427,10 @@ class ARM(ARMCommon):
     def get_kernel_offset(kernel):
         return 0
 
+    @staticmethod
+    def default_decompression_factor():
+        return 4
+
 
 class ARM64(ARMCommon):
     name = 'arm64'
@@ -442,6 +448,10 @@ class ARM64(ARMCommon):
         (text_offset,) = struct.unpack_from('<Q', kernel.read(8))
         return text_offset
 
+    @staticmethod
+    def default_decompression_factor():
+        return 1
+
 
 def resolve_arch(defined_arch=None):
     arch_classes = {'x86': X86, 'arm': ARM, 'arm64': ARM64, None: None}