mtd: rawnand: stm32_fmc2: manage all errors cases at probe time

This patch defers its probe when the expected reset control is not
yet ready. This patch also handles properly all errors cases at probe
time.

Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1588756279-17289-2-git-send-email-christophe.kerello@st.com