refactor(st): move SDMMC definitions to driver

Those specific SDMMC definitions are only used in stm32_sdmmc2.c driver.
Move them there.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: Iac7e505e9421aa7630bee8ce6fc2277b98581995
2 files changed