arm: mvebu: a37xx: Fix calling build_mem_map()

arm: mvebu: a37xx: Fix calling build_mem_map()

Function build_mem_map() modifies global variable mem_map. This variable is
used by the get_page_table_size() function which is called by function
arm_reserve_mmu() (as aliased macro PGTABLE_SIZE). Function
arm_reserve_mmu() is called earlier than enable_caches() which calls
build_mem_map(). So arm_reserve_mmu() does not calculate reserved memory
correctly.

Fix this issue by calling build_mem_map() from a3700_dram_init() which is
called before arm_reserve_mmu().

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Marek Behún <marek.behun@nic.cz>