linux-qemu.config here is based on https://github.com/u-root/webboot/…

…blob/78c6cf99a32d82b106cc373280df9512d6e25131/config-5.6.14, minus deactivating all uneeded network drivers but intel ones for Q35.

Changes of kexec-boot to pass 32 bit entry point + noefi is based on understanding of below comments.

Keeping traces of testings traces

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From linuxboot#1351 (comment)

Knowledge on related concerns seem to have made its way through webboot commits already in the past:

One of them is the following (old, talking about kernel 4.x), touching kernel graphics requirements and kexec (commit log is pretty instructing on how kernel 16->32 bits -> 64 bits works). THIS IS EXACTLY OUR ISSUE HERE:
u-root/webboot@ac6873c

The other was about setting up kexec to enter kernel through 32 bit entry point to respect kernel asking BIOS for its config:
u-root/webboot@dfc1429