remove from pub api

new() now resets the opamp and enables its clock. The clock is
disabled when the opamp is dropped. On families that use
SYSCFGEN (F3 and G4), this is not done because this
clock is always on in Embassy.

This change makes use of the RCC driver, which uses a reference
counter to prevent conflicts. The opamp itself is still disabled
when its output is dropped.

Stm32 can data len

Some trivial enums have been removed from the OpAmp API in stm32-metapac,
this commit updates the HAL accordingly.

Signed-off-by: Ivan Li <ivanli2048@gmail.com>