x86/intel_rdt: Export the minimum number of set mask bits in sysfs

x86/intel_rdt: Export the minimum number of set mask bits in sysfs

The minimum number of bits set for a cache mask is checked by the kernel
when writing a mask, but there is no way for the user to retrieve this
information.

Add a new file 'min_cbm_bits' to the info directory and export the
information to user space.

[ tglx: Massaged changelog ]
Signed-off-by: Shaohua Li <shli@fb.com>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Link: http://lkml.kernel.org/r/e69b1ffa206d0353eea58101e1bf9b677d9732f7.1478207143.git.shli@fb.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>