mmc: atmel_sdhci: re-enable sdhci after SD Card re-insertion

Whenever the SD Card would be removed and then re-inserted while in the
U-Boot command line, the `SDBPWR` bit of the `SDMMC_PCR` register would
remain unset afterwards. In order for the bit to be set again after
re-insertion, register an additional `deferred_probe` method that the
DM would then transparently call. This method will call the generic
`sdhci_probe` which will, during its execution flow, set this bit to 1.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reported-by: Mihai Sain <mihai.sain@microchip.com>
Reviewed-by: Eugen Hristev <eugen.hristev@microchip.com>