board/ti: Update MAINTAINERS entries with more boards

A few config files have been added without updating MAINTAINERS.

Reported-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/ti/am43xx/MAINTAINERS b/board/ti/am43xx/MAINTAINERS
index 3d40b17..96ef85b 100644
--- a/board/ti/am43xx/MAINTAINERS
+++ b/board/ti/am43xx/MAINTAINERS
@@ -7,3 +7,5 @@
 F:	configs/am43xx_evm_qspiboot_defconfig
 F:	configs/am43xx_evm_ethboot_defconfig
 F:	configs/am43xx_evm_usbhost_boot_defconfig
+F:	configs/am437x_gp_evm_defconfig
+F:	configs/am437x_sk_evm_defconfig