acpi: 'hw.acpi.s4bios' sysctl: Change type to bool, expand description

[olce]

Summary

Another boolean, indicating hardware support, will be introduced in next commit.

Thanks to the previous commit modifying sysctl_handle_bool(), this
change is backwards-compatible with old programs using an integer in and
out of sysctl(3).

[olce]

I'm not too sure about changing the type of a sysctl knob that has existed for a long time. The only compatibility problem that I can see doing this is potentially breaking reporting in an application that would call sysctl(3) (or sysctlbyname(3)) directly, passing an unitialized integer and then reading from it, as only the first byte would have been filled. Setting the boolean would still work (except on big-endian arches). The use of an old sysctl(8) utility is not affected.

If you feel that's not OK, I could change that part of the commit if necessary, introducing a specific handler to paper over the difference between the sysctl knob type and the field's one.

[obiwac]

Accepting assuming no one has objections about changing the size of the sysctl

[olce]

• Impacts of new prerequisite (D54926)
• Slightly tweak the description of 'hw.acpi.s4bios'

[olce]

Update commit message