dts: bcm2711: EMMC2 can address the whole first GB

Although 0xfc000000 looks like an inaccessible RAM address (due to the
peripheral mappings), with RAM mapped at 0xc0000000 (as it is on the
30/32-bit VPU bus) this is actually 0x3c000000 in the ARM memory space,
which is fine.

This difference is potentially the cause of some warnings seen in
sdhci_send_command.

Fixes: "dts: bcm2711: Move emmc2 to its own 'bus'"

Signed-off-by: Phil Elwell <phil@raspberrypi.com>