Bug#961590: d-i: add 'panfrost' to 'fb-modules' so graphical installer can be used

[Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>]

Package: linux
Severity: important
Tags: d-i

Devices with Mali gpu can use 'panfrost' driver to provide working
framebuffer. And then Debian installer can be run on screen instead of
serial console.

But 'panfrost' module is not available when d-i starts ;(

So please include 'panfrost' in 'fb-modules' udeb.

-- System Information:
Debian Release: 10.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.6.13-300.fc32.x86_64 (SMP w/12 CPU cores)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE=C (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: unable to detect