target/ppc: Drop use of gdb_get_float64() and ldfq_p()

We used to make a distinction between 'float64'/'float32' types and
the 'uint64_t'/'uint32_t' types, requiring special conversion
operations to go between them.  We've now dropped this distinction as
unnecessary, and the 'float*' types remain primarily for
documentation purposes when used in places like the function
prototypes of TCG helper functions.

This means that there's no need for a special gdb_get_float64()
function to write a float64 value to the GDB protocol buffer; we can
just use gdb_get_reg64().

Similarly, for reading a value out of the GDB buffer into a float64
we can use ldq_p() and need not use ldfq_p().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20210208113428.7181-4-peter.maydell@linaro.org>
Message-Id: <20210211122750.22645-13-alex.bennee@linaro.org>