[EC] Unify scalar multiplication for P-256/384/521 #2887

Job	Run time
grpc	25m 5s
haproxy	3m 9s
ntp	2m 7s
Python main	3m 45s
Python releases (FIPS=0 OPENSSL_IN_CRT=0)	12m 14s
Python releases (FIPS=1 OPENSSL_IN_CRT=0)	12m 22s
socat	7m 6s
tcpdump	1m 43s
Python releases (FIPS=0 OPENSSL_IN_CRT=1)	11m 54s
Python releases (FIPS=1 OPENSSL_IN_CRT=1)	11m 48s
tpm2-tss	1m 30s
trousers	1m 17s
bind9	5m 14s
libevent	27m 55s
OpenLDAP	16m 55s
strongswan	1m 43s
	2h 25m 47s

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