net: ipa: move ipa_aggr_granularity_val()

We only use ipa_aggr_granularity_val() inside "ipa_main.c", so it
doesn't really need to be defined in a header file.  It makes some
sense to be grouped with the register definitions, but it is unlike
the other inline functions now defined in "ipa_reg.h".  So move it
into "ipa_main.c" where it's used.  TIMER_FREQUENCY is used only
by that function, so move that definition as well.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>