TCPMv2: Refactor DPM_REQUEST_DR_SWAP handler.
TCPMv2: Refactor DPM_REQUEST_DR_SWAP handler.

Move DPM_REQUEST_DR_SWAP to common_src_snk_dpm_requests.

BUG=None
BRANCH=NONE
TEST=zmake testall

Signed-off-by: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>
Change-Id: I30d1411a16b0a6ca4520b8fa80aee51d72c65d8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3591302
Reviewed-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec