ARM: stm32mp: Fix dram_bank_mmu_setup() for ram_top=0

ARM: stm32mp: Fix dram_bank_mmu_setup() for ram_top=0

On STM32MP15xx with 1 GiB of DRAM, the gd->ram_top becomes 0,
because DRAM base 0xc0000000 + DRAM size 0x40000000 leads to
gd->ram_top overflow which resets it to 0. Handle this special
case simply by checking for gd->ram_top being zero, and if it
is, assume there is no addr >= gd->ram_top .

This fixes boot hang on STM32MP15xx with 1 GiB of DRAM.

Fixes: 25fb58e88aba ("ARM: stm32mp: Fix dram_bank_mmu_setup() for LMB located above ram_top")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>