qcacld-3.0: Add microseconds to BUILD_TAG

Some of the post processing tools need high resolution timestamps in the
build tag to differentiate WLAN driver modules in the same build. Add
current time with nanoseconds rounded to the first 6 digits, which is
microseconds. Also fix the 'date' command format.

e.g. date -u +'%F %T.%N %Z'
     2020-06-25T17:40:43.919224370 UTC

Change-Id: Ie2a8af4dad2aead5738a4c710a201fe9674999f7
CRs-Fixed: 2719008

Kbuild

@@ -3616,8 +3616,12 @@ CMN_IDS = $(shell cd "$(WLAN_COMMON_INC)" && \
 	git log -50 $(CMN_CHECKOUT)~..HEAD | \
 		sed -nE 's/^\s*Change-Id: (I[0-f]{10})[0-f]{30}\s*$$/\1/p' | \
 		paste -sd "," -)
-
-TIMESTAMP = $(shell date -u +'%Y-%m-%dT%H:%M:%SZ')
+# date -u +'%F %T.%6N %Z'
+#	%F  : Full date
+#	%T  : Time
+#	%6N : Nanoseconds to 6 digits
+#	%Z  : Time zone
+TIMESTAMP = $(shell date -u +'%F %T.%6N %Z')
 BUILD_TAG = "$(TIMESTAMP); cld:$(CLD_IDS); cmn:$(CMN_IDS);"
 # It's assumed that BUILD_TAG is used only in wlan_hdd_main.c
 CFLAGS_wlan_hdd_main.o += -DBUILD_TAG=\"$(BUILD_TAG)\"