Update EC commit, improvements to bitbanging

This update improves the accuracy of DAC and ADC functionality, and
introduces a feature to generate arbitrary waveforms by re-using the
bitbanging timer interrupt and other infrastructure to set DAC output
values at fixed intervals.  Also, bitbanging speed is improved by means
of just-in-time composing an interrupt handler from fragments of machine
code.

2eac9058cd board/hyperdebug: ADC calibration
534f66f698 board/hyperdebug: Support dac-banging
d49a60e34d board/hyperdebug: Optimize bitbanging
457943a081 board/hyperdebug: Rename of bitbang variables
382f9404d2 board/hyperdebug: Refactor interrupt vector table
61302f0ff7 board/hyperdebug: Support PWM signal generation

third_party/chromium/repos.bzl

@@ -8,7 +8,7 @@ def chromium_repos():
     git_repository(
         name = "ec_src",
         remote = "https://chromium.googlesource.com/chromiumos/platform/ec",
-        commit = "37c9854cbacd275e714491c65018e151fb22d1a6",
+        commit = "2eac9058cd6fb4e8baf687ec67fe9a128eb8d08f",
         build_file = "//third_party/chromium:BUILD.ec_src.bazel",
         patches = [
             "//third_party/chromium:ec-custom-version.patch",