x86/vm86: Fix the misleading CONFIG_VM86 Kconfig help text

x86/vm86: Fix the misleading CONFIG_VM86 Kconfig help text

The CONFIG_VM86 Kconfig help text is actively misleading, so fix it:

  - Don't mark it 'obsolete' in the text as we'll support the ABI as long as CPUs
    support it.

  - Qualify the part about software emulation and mention that for some apps you
    want a real vm86 mode.

  - Don't scare users away from the option, instead explain what it does.

Reported-by: Stas Sergeev <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Austin S Hemmelgarn <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Josh Boyer <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Matthew Garrett <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>