mmc: esdhc: Fix bug when writing to SDHCI_HOST_CONTROL register

The P2020 has a non-standard implementation of the SDHCI_HOST_CONTROL
register. This patch adds a QUIRK in the SDHCI header to signal that
a host controller has a non-standard SDHCI_HOST_CONTROL register. The
patch adds a check to the function esdhc_writeb in file
sdhci-of-esdhc.c, where it checks if the write is done to the
SDHCI_HOST_CONTROL register and th host has the above mentioned QUIRK,
then the function simply returns instead of writing to the register.
The patch also detects if the processor is P2020 (by looking in dev
tree) and if so, adds the QUIRK to the host->quirk2

Signed-off-by: Oded Gabbay <ogabbay@advaoptical.com>
Reviewed-by: Anton Vorontsov <anton@enomsg.org>
Signed-off-by: Chris Ball <cjb@laptop.org>