[23.05] backport "luci-app-attendedsysupgrade: add x86 efi/bios case" (#6623)

[23.05] backport "luci-app-attendedsysupgrade: add x86 efi/bios case" (#6623)

* luci-app-attendedsysupgrade: add x86 efi/bios case

x86 is the only target that allows you to install either EFI or BIOS
images, thereby add an extra check for that.

Signed-off-by: Paul Spooren <mail@aparcar.org>
(cherry picked from commit d7e905e83a11d59ea217cd37189040bd6c9d403e)

* luci-app-attendedsysupgrade: fix search for x86 target

The conditional is wrong. IndexOf returns a number and not true/false,
so it does not work.

Signed-off-by: Miguel Angel Mulero Martinez <migmul@gmail.com>
(cherry picked from commit 021c4394871e062964e1601775f4c951d0e2b878)

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Co-authored-by: Paul Spooren <mail@aparcar.org>
Co-authored-by: Miguel Angel Mulero Martinez <migmul@gmail.com>