ftrace: Use macros for numbers in ftrace rec shift bits

As new flags will be added to the ftrace dynamic record, and since
the flags field is also a counter, converting the numbers used to
do the shifting and masking into a set of macros where we only need
to deal with the max bit count of the counter and the number of bits
for the flags will prevent mistakes in the future.

Dealing with only two numbers is much easier than updating all the
macros that deal with shifting and masking.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>