flash: stm32: fix g0 error flags and move ifdef-ery to header

In STM32G0 HAL FLASH_FLAG_xxx defines don't follow the pattern of
other Series to simply redefine the FLASH_SR_xxx Msk.
Instead an ID for the SR reg and the position of the Error flag
are defined.

As a result error checking in flash_stm32_check_status was not working
until this fix on stm32g0 series.

In order to avoid complexity in the driver, the ifdef-ery of the flags
was moved to the header file.
Other series except g0 use FLASH_FLAG_xxx defines, because those
are valid for both cores in dual core(wl) and in secure/non-secure
targets(l5,u5).
FLASH_STM32_SR_ERRORS mask is introduced to check for any active error
in the SR.

The flags for SIZERR, MISERR, FASTERR are newly introduced.
the latter two are only required once fast programming is used,
which is not yet the case for any series.

The FLASH_SR_OPTVERR flag (option validity flag) is also present
in the SR, but is not added.
Also ecc errors are generally not checked, but these are in a different
register.

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>