board_f: Fix types for board_get_usable_ram_top()

Commit 37dc958947ed ("global_data.h: Change ram_top type to phys_addr_t")
changed type of ram_top member from ulong to phys_addr_t but did not
changed types in board_get_usable_ram_top() function which returns value
for ram_top.

So change ulong to phys_addr_t type also in board_get_usable_ram_top()
signature and implementations.

Fixes: 37dc958947ed ("global_data.h: Change ram_top type to phys_addr_t")
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/include/asm/mrc_common.h b/arch/x86/include/asm/mrc_common.h
index 3d7f00c..a7f260a 100644
--- a/arch/x86/include/asm/mrc_common.h
+++ b/arch/x86/include/asm/mrc_common.h
@@ -47,7 +47,7 @@
  * the relocation address, and how far U-Boot is moved by relocation are
  * set in the global data structure.
  */
-ulong mrc_common_board_get_usable_ram_top(ulong total_size);
+phys_size_t mrc_common_board_get_usable_ram_top(phys_size_t total_size);
 
 void mrc_common_dram_init_banksize(void);