Bug#773311: confusing dialogue on lack of EFI system partition on non-x86

[Leif Lindholm <leif.lindholm@linaro.org>]

Package: partman-efi
Severity: wishlist

When attempting to install Jessie (daily snapshot from today) on
arm64, with an already partitioned disk without an EFI System
Partition, the following dialogue appears:
---
  │ This machine's firmware has started the installer in UEFI mode but it │
  │ looks like there may be existing operating systems already installed  │
  │ using "BIOS compatibility mode". If you continue to install Debian in │
  │ UEFI mode, it might be difficult to reboot the machine into any       │
┌│ BIOS-mode operating systems later.                                    │
│ │                                                                       │
│ │ If you wish to install in UEFI mode and don't care about keeping the  │
│ │ ability to boot one of the existing systems, you have the option to   │
│ │ force that here. If you wish to keep the option to boot an existing   │
│ │ operating system, you should choose NOT to force UEFI installation    │
└│ here.                                                                 │
  │                                                                       │
  │ Force UEFI installation?                                              │
---

Since there never existed a "BIOS compatibility mode" on arm64, this
message is quite misleading.
Could we simply suppress this message on non-x86? Lack of an EFI
system partition would make itself known later on anyway.