board: gaisler: delete unnecessary include path

The same outputs are generated with or without -I$(TOPDIR)/board.
I cannot understand why it is necessary. Remove.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Daniel Hellstrom <daniel@gaisler.com>
diff --git a/board/gaisler/gr_cpci_ax2000/config.mk b/board/gaisler/gr_cpci_ax2000/config.mk
index 309c879..731a539 100644
--- a/board/gaisler/gr_cpci_ax2000/config.mk
+++ b/board/gaisler/gr_cpci_ax2000/config.mk
@@ -17,5 +17,3 @@
 
 # U-BOOT IN SDRAM
 #CONFIG_SYS_TEXT_BASE = 0x60000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board
diff --git a/board/gaisler/gr_ep2s60/config.mk b/board/gaisler/gr_ep2s60/config.mk
index d57efae..6e01f07 100644
--- a/board/gaisler/gr_ep2s60/config.mk
+++ b/board/gaisler/gr_ep2s60/config.mk
@@ -15,5 +15,3 @@
 
 # U-BOOT IN SDRAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board
diff --git a/board/gaisler/gr_xc3s_1500/config.mk b/board/gaisler/gr_xc3s_1500/config.mk
index e87320b..e4a66cb 100644
--- a/board/gaisler/gr_xc3s_1500/config.mk
+++ b/board/gaisler/gr_xc3s_1500/config.mk
@@ -14,5 +14,3 @@
 
 # U-BOOT IN RAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board
diff --git a/board/gaisler/grsim/config.mk b/board/gaisler/grsim/config.mk
index df26f82..d1f61da 100644
--- a/board/gaisler/grsim/config.mk
+++ b/board/gaisler/grsim/config.mk
@@ -14,5 +14,3 @@
 
 # U-BOOT IN RAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board
diff --git a/board/gaisler/grsim_leon2/config.mk b/board/gaisler/grsim_leon2/config.mk
index 99f9a68..f98b23b 100644
--- a/board/gaisler/grsim_leon2/config.mk
+++ b/board/gaisler/grsim_leon2/config.mk
@@ -14,5 +14,3 @@
 
 # RUN U-BOOT FROM RAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board