Create separate modules for i2c_bitbang and bpf_filter so these files
can be included in kernels which need them without also duplicating
them in other modules. Removes the duplicate symbols I found which
prevented loading i2c and bpf modules after having fixed PR 45125.

branches: 1.13.36;
Fix typo in comments.

branches: 1.12.14; 1.12.16;
Set SDA High (it means turning off open-collector driver
regardless of DIR() on the formal I2C hardware implementation)
during DIR() is set to INPUT. Some MD drivers might assume it.

tl(4) still works with this change.

branches: 1.11.2; 1.11.4;
Reorganize I2C bitbang ops:
- don't set DIR(INPUT) in i2c_wait_for_scl() because it could cause
unexpected stop condition in SCL=H, SDL=L and DIR(OUTPUT) case,
and DIR() should be used only to switch SDA direction, not SCL
that is always output on the master device
(I'm not sure if reading SCL on the master is defined in the I2C spec)
- set SDA right after SCL H->L edge on Tx, fetch SDA at SCL L->H edge on Rx,
and make sure not to change SDA during SCL=H except start/stop conditions
so that we don't have to rely on data setup time which might be critical
- don't set DIR(OUTPUT) during SDA bit read in i2c_bitbang_read_byte()
- explicitly specify both SDA and SCL bits in SETBITS() for readability
- sprinkle comments

Fixes "tl0: error reading Ethernet address" problem on tl(4).

- use 'us' for microsecond rather than 'uS'
- unwrap not so long lines
- some KNF

branches: 1.9.8; 1.9.10; 1.9.12; 1.9.14;
use __KERNEL_RCSID()

branches: 1.8.2; 1.8.4; 1.8.6;
Fix lost direction for the check on status, and read/writes.

branches: 1.7.6; 1.7.8; 1.7.14;
add support for i2c waitstates so we can actually talk to slow slaves
Suggestions and review by simon

branches: 1.6.4; 1.6.8; 1.6.10;
__unused removal on arguments; approved by core.

- sprinkle __unused on function decls.
- fix a couple of unused bugs
- no more -Wno-unused for i386

branches: 1.4.4; 1.4.6;
Add support for 10-bit addressing, per i2c specs. This has not been tested
with any actual 10-bit devices (as I don't have any), but it doesn't seem to
impact 7-bit addressing any. Approved by christos@, briggs@, and thorpej@.

branches: 1.3.8;
cleanup more SET/CLR/ISSET lossage

branches: 1.2.4; 1.2.6; 1.2.8;
merge ktrace-lwp.

branches: 1.1.4; 1.1.18;
New generic I2C framework. Supports bit-bang and "intelligent" I2C
interface controllers (of varying intelligence levels).

Contributed by Wasabi Systems, Inc. Primarily written by Steve Woodford,
with some modification by me.