x86/bitops: Use __builtin_constant_p() directly instead of IS_IMMEDIATE()

__builtin_constant_p(nr) is used everywhere now. It does not make much
sense to define IS_IMMEDIATE() as its alias.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190723074415.26811-1-yamada.masahiro@socionext.com