[POWERPC] Don't use HOSTCFLAGS in BOOTCFLAGS

In the bootwrapper code for powerpc, we include HOSTCFLAGS into the
BOOTCFLAGS used for building the zImage wrapper code.  Since the
wrapper code is not host code, this makes no sense.  This patch
removes the use of HOSTCFLAGS here, instead including directly into
BOOTCFLAGS those flags from the normal kernel CFLAGS which also make
sense in the bootwrapper code.

In particular, this makes the bootwrapper use -msoft-float, preventing
the compiler from generating floating point instructions.  Previously,
under some circumstances the compiler could generate floating point
instructions in the bootwrapper which would cause exceptions on
embedded CPUS which don't have floating point support.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>