common: pd_log: Add PD log to .bss.slow.
common: pd_log: Add PD log to .bss.slow.

BUG=chrome-os-partner:46056
BUG=chrome-os-partner:46063
BRANCH=None
TEST=Enable CONFIG_REPLACE_LOADER_WITH_BSS_SLOW on GLaDOS.  Build,
flash, and verify that AP and EC boot.  Plug in a charger on both ports
and use ectool to view the PD log.
TEST=make -j buildall tests

CQ-DEPEND=CL:311209

Change-Id: I54ae617e03c645d24319d83da6cc8b7d1d6528a3
Signed-off-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@google.com>
Reviewed-on: https://chromium-review.googlesource.com/311413
Commit-Ready: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Tested-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Reviewed-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>

coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics