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: NMasahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Daniel Hellstrom <daniel@gaisler.com>

board/gaisler/gr_cpci_ax2000/config.mk

@@ -17,5 +17,3 @@ CONFIG_SYS_TEXT_BASE = 0x00000000
 
 # U-BOOT IN SDRAM
 #CONFIG_SYS_TEXT_BASE = 0x60000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board

board/gaisler/gr_ep2s60/config.mk

@@ -15,5 +15,3 @@ CONFIG_SYS_TEXT_BASE = 0x00000000
 
 # U-BOOT IN SDRAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board

board/gaisler/gr_xc3s_1500/config.mk

@@ -14,5 +14,3 @@ CONFIG_SYS_TEXT_BASE = 0x00000000
 
 # U-BOOT IN RAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board

board/gaisler/grsim/config.mk

@@ -14,5 +14,3 @@ CONFIG_SYS_TEXT_BASE = 0x00000000
 
 # U-BOOT IN RAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board

board/gaisler/grsim_leon2/config.mk

@@ -14,5 +14,3 @@ CONFIG_SYS_TEXT_BASE = 0x00000000
 
 # RUN U-BOOT FROM RAM
 #CONFIG_SYS_TEXT_BASE = 0x40000000
-
-PLATFORM_CPPFLAGS += -I$(TOPDIR)/board