net: ipa: reg: include <linux/bug.h>

When "reg.h" got created, it included calls to WARN() and WARN_ON().
Those macros are defined via <linux/bug.h>.  In addition, it uses
is_power_of_2(), which is defined in <linux/log2.h>.  Include those
files so IPA "reg.h" has access to all definitions it requires.

Meanwhile, <linux/bits.h> is included but nothing defined therein
is required directly in "reg.h", so get rid of that.

Fixes: 81772e44 ("net: ipa: start generalizing "ipa_reg"")
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>