Problem installing driver for kernel 5.15

[tbisanz]

Tried installing this driver under a somewhat current Ubuntu 22 LTS release; encountered the following problems:

• HAVE_UNLOCKED_IOCTL is no longer defined (since 5.9 or so, c.f.: torvalds/linux@4e24566)
• In Linux kernel 5.8, the mmap_sem member of struct mm_struct was renamed to mmap_lock and a new mmap locking API was added. (c.f. post here by Ian Abbott: https://stackoverflow.com/questions/71600159/struct-mm-struct-has-no-member-named-mmap-sem-error-in-the-module-build-afte )
• And there is an issue where presumably ... task_size_max() inline, which uses X86_FEATURE_LA57, but doesn't include <asm/cpufeatures.h> which defines the constant was added (c.f. https://lore.kernel.org/lkml/163855309686.11128.8994895456821800765.tip-bot2@tip-bot2/T/)

In my fork there is a branch which has these things hacked together (e.g. just defining HAVE_UNLOCKED_IOCTL in a very bad way instead of providing a proper kernel version check and a mmap_sem pre 5.8 interface taken 1:1 from stackoverflow), I would not want to merge this in, but it might help others: tbisanz@be94acc