Kconfig: CPU_MIGHT_SUPPORT_CLFLUSH removal.

Remove CPU_MIGHT_SUPPORT_CLFLUSH as excessive.

Removal the flag requires adding per-SoC cnfiguration,
as some Quark models support clflush instruction, but
some do not, even on compiler level.

Change-Id: I655cba00c629db55d1813c199a2fe08b2d60ef4f
Signed-off-by: Dmitriy Korovkin <dmitriy.korovkin@windriver.com>