tests: llext: RISC-V Tests not run due to missing RAM attribute

[WorldofJARcraft]

Describe the bug

Commit 816a7a0 introduced a filtering by RAM/Flash size for llext tests. Currently, none of the RISC-V qemu boards provides this information, so llext tests on RISC-V are not run.

To Reproduce
Attempt to run llext tests on RISC-V:

west  twister  -a riscv -p qemu_riscv64  -T tests/subsys/llext/

No test actually runs, as they are statically filtered.
It appears that the tests also do not run in CI.

Expected behavior

It should be possible to run the RISC-V tests manually, and they should be executed in CI.

Impact

llext's architecture-specific code for RISC-V is not tested.

Logs and console output

This is from my PR #82799 when running with -y (test plan only) and -v -v -v.
`
INFO - Using Ninja..
INFO - Zephyr version: v4.1.0-rc1-46-g37f5100b6708
INFO - Using 'zephyr' toolchain.
INFO - Building initial testsuite list...
INFO - Writing JSON report /home/worldofjarcraft/Projects/zephyrproject/zephyr/twister-out/testplan.json
INFO - JOBS: 16
INFO - Adding tasks to the queue...
INFO - Added initial list of jobs to queue

INFO - 1 test scenarios (1 configurations) selected, 1 configurations filtered (1 by static filter, 0 at runtime).
Summary
├── Total test suites: 1
├── Processed test suites: 1
│ ├── Filtered test suites: 1
│ │ ├── Filtered test suites (static): 1
│ │ └── Filtered test suites (at runtime): 0
│ └── Selected test suites: 0
│ ├── Skipped test suites: 0
│ ├── Passed test suites: 0
│ ├── Built only test suites: 0
│ ├── Failed test suites: 0
│ └── Errors in test suites: 0
└── Total test cases: 9
├── Filtered test cases: 9
└── Selected test cases: 0
├── Passed test cases: 0
├── Skipped test cases: 0
├── Built only test cases: 0
├── Blocked test cases: 0
├── Failed test cases: 0
└── Errors in test cases: 0
INFO - 0 of 0 executed test configurations passed (0.00%), 0 built (not run), 0 failed, 0 errored, with no warnings in 1.58 seconds.
INFO - 0 of 0 executed test cases passed (0.00%) on 0 out of total 948 platforms (0.00%).
INFO - 0 test configurations executed on platforms, 0 test configurations were only built.
INFO - Saving reports...
INFO - Writing JSON report /home/worldofjarcraft/Projects/zephyrproject/zephyr/twister-out/twister.json
INFO - Writing xunit report /home/worldofjarcraft/Projects/zephyrproject/zephyr/twister-out/twister.xml...
INFO - Writing xunit report /home/worldofjarcraft/Projects/zephyrproject/zephyr/twister-out/twister_report.xml...
INFO - Run completed
`

Environment (please complete the following information):

• OS: Linux (ubuntu 22.04 LTS)
• Toolchain Zephyr SDK: 0.16.8
• Commit SHA or Version used: 2ce2794