PEL: Add BCD time helpers for PELs

A PEL stores time in BCD, with a byte each for:
* year MSB
* year LSB
* month
* day
* hour
* minutes
* seconds
* hundredths

This commit adds a structure to represent this, and functions to:
* Create a BCD structure from a std::chrono::time_point
* Convert any number to BCD
* Write the BCD structure into a Stream
* Extract a BCD structure from a Stream

Refresher: The BCD value of 32 is 0x32.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I09ea4098f3a3981931f595d11fb63aff31d9fb0d
diff --git a/extensions/openpower-pels/openpower-pels.mk b/extensions/openpower-pels/openpower-pels.mk
index 1030171..94c7bb8 100644
--- a/extensions/openpower-pels/openpower-pels.mk
+++ b/extensions/openpower-pels/openpower-pels.mk
@@ -1,4 +1,5 @@
 phosphor_log_manager_SOURCES += \
+	extensions/openpower-pels/bcd_time.cpp \
 	extensions/openpower-pels/entry_points.cpp \
 	extensions/openpower-pels/manager.cpp