x86/Kconfig: Further simplify the NR_CPUS config

x86/Kconfig: Further simplify the NR_CPUS config

Clean up various aspects of the x86 CONFIG_NR_CPUS configuration switches:

- Rename the three CONFIG_NR_CPUS related variables to create a common
  namespace for them:

    RANGE_BEGIN_CPUS => NR_CPUS_RANGE_BEGIN
    RANGE_END_CPUS   => NR_CPUS_RANGE_END
    DEF_CONFIG_CPUS  => NR_CPUS_DEFAULT

- Align them vertically, such as:

    config NR_CPUS_RANGE_END
            int
            depends on X86_64
            default 8192 if  SMP && ( MAXSMP ||  CPUMASK_OFFSTACK)
            default  512 if  SMP && (!MAXSMP && !CPUMASK_OFFSTACK)
            default    1 if !SMP

- Update help text, add more comments.

Test results:

 # i386 allnoconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=1
 CONFIG_NR_CPUS_RANGE_END=1
 CONFIG_NR_CPUS_DEFAULT=1
 CONFIG_NR_CPUS=1

 # i386 defconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=2
 CONFIG_NR_CPUS_RANGE_END=8
 CONFIG_NR_CPUS_DEFAULT=8
 CONFIG_NR_CPUS=8

 # i386 allyesconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=2
 CONFIG_NR_CPUS_RANGE_END=64
 CONFIG_NR_CPUS_DEFAULT=32
 CONFIG_NR_CPUS=32

 # x86_64 allnoconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=1
 CONFIG_NR_CPUS_RANGE_END=1
 CONFIG_NR_CPUS_DEFAULT=1
 CONFIG_NR_CPUS=1

 # x86_64 defconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=2
 CONFIG_NR_CPUS_RANGE_END=512
 CONFIG_NR_CPUS_DEFAULT=64
 CONFIG_NR_CPUS=64

 # x86_64 allyesconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=8192
 CONFIG_NR_CPUS_RANGE_END=8192
 CONFIG_NR_CPUS_DEFAULT=8192
 CONFIG_NR_CPUS=8192

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180210113629.jcv6su3r4suuno63@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>