tegra: correct cpu subtype

tegra: correct cpu subtype

Tegra 2 processors have only 16 double-precision registers. The change
introduced by 8dcc1087602e ("toolchain: ARM: Fix toolchain compilation
for gcc 8.x") switched accidentally the toolchain for tegra target to cpu
type with 32 double-precision registers. This stems from gcc defaults
which assume "vfpv3-d32" if only "vfpv3" as mfpu is specified. That
change resulted in unusable image, in which kernel will kill userspace as
soon as it causing "Illegal instruction".

Ref: https://forum.openwrt.org/t/gcc-was-broken-on-mvebu-armada-370-device-after-commit-on-2019-03-25/43272
Fixes: 8dcc1087602e ("toolchain: ARM: Fix toolchain compilation for
gcc 8.x")
Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>