[Hexagon] NFC: Flatten calling conventions (#234977)
Hexagon calling conventions had conditions based on enabled ISA
extensions. These conditions were effectively checked twice: once in the
C backend code which selected which CC to use and another time by
conditions in the CC itself e.g. CCIfHvx64, CCIfHvx128.
Flatten the calling conventions into one and remove the checks in the
backend code.
Signed-off-by: Alexey Karyakin <akaryaki@qti.qualcomm.com>
