board/adp-ag102: add configuration of adp-ag102

board:
Add config file of board adp-ag102
Add adp-ag102 into boards.cfg
Add adp-ag102 into MAINTAINERS

doc:
add README of ag102

Signed-off-by: Macpaul Lin <macpaul@andestech.com>
diff --git a/boards.cfg b/boards.cfg
index 3cf75c3..3b8be87 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -370,6 +370,7 @@
 qi_lb60                      mips        xburst      qi_lb60             qi
 adp-ag101                    nds32       n1213       adp-ag101           AndesTech      ag101
 adp-ag101p                   nds32       n1213       adp-ag101p          AndesTech      ag101
+adp-ag102                    nds32       n1213       adp-ag102           AndesTech      ag102
 nios2-generic                nios2       nios2       nios2-generic       altera
 PCI5441                      nios2       nios2       pci5441             psyent
 PK1C20                       nios2       nios2       pk1c20              psyent