pci_handler: Add pci_handler

Taken most of the logic from phoshpor-ipmi-flash:
https://github.com/openbmc/phosphor-ipmi-flash/blob/master/tools/io.cpp

Tested: Unit Test + Tested this on a real machine

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I546d1dff8764e31c9f2fa6c7465ba23a24f6fdea
diff --git a/subprojects/fmt.wrap b/subprojects/fmt.wrap
new file mode 100644
index 0000000..6847ae5
--- /dev/null
+++ b/subprojects/fmt.wrap
@@ -0,0 +1,3 @@
+[wrap-git]
+url = https://github.com/fmtlib/fmt
+revision = HEAD