Increase size of EFI system partition (again)

When I said in I8594d1fe05242f246a5809740a115ab2f84ac5a3 that 12 MiB
ought to be enough, I should have expected that I would be proven wrong.
While 12 MiB is enough to fit shim-x64 and grub2-efi-x64, yum fails to
update these packages to newer versions:

Transaction check error:
  installing package shim-x64-15-2.el7.centos.x86_64 needs 7MB on the /boot/efi filesystem
  installing package grub2-efi-x64-1:2.02-0.76.el7.centos.1.x86_64 needs 3MB on the /boot/efi filesystem

Error Summary
-------------
Disk Requirements:
  At least 7MB more space needed on the /boot/efi filesystem.

It is recommended that the ESP partition be much bigger. This commit
bumps its size to 550MiB, following guidelines from Rod Smith to avoid
incompatibilities with some EFIs [1].

[1] https://www.rodsbooks.com/efi-bootloaders/principles.html

Change-Id: If9515234f1a803cda32b2482f8abe10ddf0e6d26

diskimage_builder/elements/block-device-efi/block-device-default.yaml

@@ -7,7 +7,7 @@
     partitions:
       - name: ESP
         type: 'EF00'
-        size: 12MiB
+        size: 550MiB
         mkfs:
           type: vfat
           mount:

releasenotes/notes/gpt-esp-partition-size-200568cb6fcc8788.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The size of the ESP partition when building EFI based images is increased
+    considerably from 12MiB to 550MiB, in line with modern guidelines.  The
+    existing size was often not enough to update packages.