mmc: update mmp2 mmc resources in arch/arm

Update MMP2 platform code to "sdhci-pxav3", following the driver rename.

Signed-off-by: Zhangfei Gao <zhangfei.gao@marvell.com>
Acked-by: Philip Rakity <prakity@marvell.com>
Acked-by: Mark F. Brown <mark.brown314@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>