dfx_dtg_common does only handle xsa files with file:-scheme in SRC_URI

[hannesweisbach]

Having a recipe inherit from dfx_dtg_zynqmp_full and then including the xsa-file with anything other than a file:-scheme fails:

| cmd is: xsct -sdx -nodisp /home/oe/build/tmp-glibc/work/linux/<cut>/1.0/dtgen_dfx.tcl -ws /home/oe/build/tmp-glibc/work/linux/<cut>/1.0/build -pname <cut> -rp /home/oe/build/tmp-glibc/work/linux/<cut>/1.0/git -processor_ip psu_cortexa53 -hdf /home/oe/build/tmp-glibc/work/linux/<cut>/1.0/http://<my-server>/path/to/my.xsa -arch 64    -hdf_type xsa -hwpname <cut> -yamlconf /home/oe/build/tmp-glibc/work/linux/<cut>/1.0/<cut>.yaml
[...]
| INFO: [Hsi 55-2053] elapsed time for repository (/home/oe/build/tmp-glibc/work/linux/<cut>/1.0/recipe-sysroot-native/Vitis/2024.2/data/embeddedsw) loading 0 seconds
| ERROR: [HDF 64-5] File not found - /home/oe/build/tmp-glibc/work/linux/<cut>/1.0/http://<myserver>/path/to/my.xsa
| ERROR: [Hsi 55-1451] Error: running open_hw_design.
| ERROR: [Common 17-39] 'hsi::open_hw_design' failed due to earlier errors.

Note: Internal naming has been redacted or altered.

Minimal recipe:

LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""

SRC_URI += "http://server/path/to/example.xsa"
SRC_URI[sha256sum] = ""

Steps to reproduction:
(1) Have an xsa on http/s or similar (artifact storage?)
(2) Create minimal recipe file
(3) Build minimal recipe