adp-ag101p: add product into MAINTAINERS list

Add ADP-AG101P into MAINTAINERS list.
Add ADP-AG101P into boards.cfg.

Signed-off-by: Macpaul Lin <macpaul@andestech.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 030fe4a..3c9dba7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1151,6 +1151,7 @@
 Macpaul Lin <macpaul@andestech.com>
 
 	ADP-AG101	N1213 (AG101 SoC)
+	ADP-AG101P	N1213 (AG101P XC5 FPGA)
 
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 # End of MAINTAINERS list						#