stm32: add SPI register definitions and refactor

refactor existing code in usb_pd_phy.c to use new register definitions

BRANCH=none
BUG=none
TEST=manually verify macro substitutions produce same value

Change-Id: Ia0cd815164b0262640425abd6da973c170163f2f
Signed-off-by: Dominic Chen <ddchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/202392
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
2 files changed