Add SAI-1.4.0 to opensource build

Summary:
- Added sai to getdeps
- added SAI to FBOSS as a dependency
- Included path of SAI headers to FBOSS's cmake file.

Reviewed By: shri-khare

Differential Revision: D18629127

fbshipit-source-id: 119a6b7f2b64bd84414d9e16a903bc8df48a35e7

build/fbcode_builder/manifests/fboss

@@ -30,6 +30,7 @@ libmnl
 libusb
 libcurl
 libnl
+libsai
 
 [shipit.pathmap]
 fbcode/fboss/github = .

build/fbcode_builder/manifests/libsai

+[manifest]
+name = libsai
+
+[download]
+url = https://github.com/opencomputeproject/SAI/archive/v1.4.0.tar.gz
+sha256 = 3eb65724b053886236c6cc408853a419fea9a0db19081e38209c2e8718b724b3
+
+[build]
+builder = nop
+subdir = SAI-1.4.0
+
+[install.files]
+inc = include