arm: select CCFPEmode for LTGT [PR91323]

arm: select CCFPEmode for LTGT [PR91323]

Besides Arm, there are three other ports that define both CCFPmode and
CCFPEmode.  AArch64 and Sparc return CCFPEmode for LTGT; the other,
Visium, doesn't support LTGT at all.

AArch64 was changed in r8-5286-g8332c5ee8c5f3b, and Sparc with
r10-2926-g000a5f8d23c04c.

I suspect this issue is latent on Arm because cbranch?f4 and cstore?f4
reject LTGT and UNEQ and we fall back to a generic expansion which
happens to work.  Nevertheless, this patch updates the relevant bits
of the Arm port to match the specification introduced in
r10-2926-g000a5f8d23c04c.

gcc/ChangeLog:

	PR target/91323
	* config/arm/arm.cc (arm_select_cc_mode): Use CCFPEmode for LTGT.