hw/misc/allwinner-h3-dramc: enforce 64-bit multiply when calculating row mirror address

The allwinner_h3_dramc_map_rows function simulates row addressing behavior
when bootloader software attempts to detect the amount of available SDRAM.

Currently the line that calculates the 64-bit address of the mirrored row
uses a signed 32-bit multiply operation that in theory could result in the
upper 32-bit be all 1s. This commit ensures that the row mirror address
is calculated using only 64-bit operations.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-id: 20200323192944.5967-1-nieklinnenbank@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>