Github removed support for the Subversion protocol

[quantabase13]

According to
https://github.blog/changelog/2024-01-08-subversion-has-been-sunset/ ,
Github has no longer support subversion protocol from 2024/01/08,
the following bash commands in cmsis.mk don't work now.

$(CMSIS)/arm:
	svn export -r$(SVN_REV) -q --force https://github.com/ARMmbed/mbed-os/trunk/cmsis/ $(CMSIS)/arm

$(CMSIS)/TARGET_STM:
	svn export -r$(SVN_REV) -q --force https://github.com/ARMmbed/mbed-os/trunk/targets/TARGET_STM/ $(CMSIS)/TARGET_STM

[jserv]

According to https://github.blog/changelog/2024-01-08-subversion-has-been-sunset/ , Github has no longer support subversion protocol from 2024/01/08, the following bash commands in cmsis.mk don't work now.

We can use shallow git submodule instead.