powerpc/e500mc: Set assembler machine type to e500mc

powerpc/e500mc: Set assembler machine type to e500mc

In binutils 2.26 a new opcode for the "wait" instruction was added for the
POWER9 and has precedence over the one specific to the e500mc. Commit
ebf714ff3756 ("powerpc/e500mc: Add support for the wait instruction in
e500_idle") uses this instruction specifically on the e500mc to work around
an erratum.

This results in an invalid instruction in idle_e500 when we build for the
e500mc on bintutils >= 2.26 with the default assembler machine type.

Since multiplatform between e500 and non-e500 is not supported, set the
assembler machine type globaly when CONFIG_PPC_E500MC=y.

Signed-off-by: Michael Jeanson <[email protected]>
Reviewed-by: Mathieu Desnoyers <[email protected]>
CC: Benjamin Herrenschmidt <[email protected]>
CC: Paul Mackerras <[email protected]>
CC: Michael Ellerman <[email protected]>
CC: Kumar Gala <[email protected]>
CC: Vakul Garg <[email protected]>
CC: Scott Wood <[email protected]>
CC: Mathieu Desnoyers <[email protected]>
CC: [email protected]
CC: [email protected]
CC: [email protected]
Signed-off-by: Michael Ellerman <[email protected]>