dm: crypto: Define UCLASS API for ECDSA signature verification

Define a UCLASS API for verifying ECDSA signatures. Unlike
UCLASS_MOD_EXP, which focuses strictly on modular exponentiation,
the ECDSA class focuses on verification. This is done so that it
better aligns with mach-specific implementations, such as stm32mp.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>