nvptx/nvptx.opt: Update -march-map= for newer sm_xxx

nvptx/nvptx.opt: Update -march-map= for newer sm_xxx

Usage of the -march-map=: "Select the closest available '-march=' value
that is not more capable."

As PTX ISA 8.6/8.7 (= unreleased CUDA 12.7 + CUDA 12.8) added the
Nvidia Blackwell GPUs SM_100, SM_101, and SM_120, it makes sense to
add them as well. Note that all three come as sm_XXX and sm_XXXa.

PTX ISA 8.8 (CUDA 12.9) added SM_103 and SM_121 and the new 'f' suffix
for all SM_1xx.

Internally, GCC currently generates the same code for >= sm_80 (Ampere);
however, as GCC's -march= also supports sm_89 (Ada), the here added
sm_1xxs (Blackwell) will map to sm_89.

[Naming note: while ptx code generated for sm_X can also run with sm_Y
if Y > X, code generated for sm_XXXa can (generally) only run on
the specific hardware; and sm_XXXf implies compatibility with only
subsequent targets in the same family.]

gcc/ChangeLog:

	* config/nvptx/nvptx.opt (march-map=): Add sm_100{,f,a},
	sm_101{,f,a}, sm_103{,a,f}, sm_120{,a,f} and sm_121{,f,a}.