arch/mips: Add support for loadable ELF modules

[ldube]

Summary

Implement architecture-specific ELF header definitions and relocation handling for the MIPS architecture to enable loadable modules.

Fixes #19178.

Changes include:

• Add arch/mips/include/elf.h with MIPS ELF relocation types and architecture-specific ELF data structures (arch_elfdata_s).
• Implement libs/libc/machine/mips/arch_elf.c containing up_checkarch, up_relocate, and up_relocateadd functions handling R_MIPS_NONE, R_MIPS_32, R_MIPS_26, R_MIPS_HI16, and R_MIPS_LO16 relocations.
• Integrate MIPS machine-specific C library support in libs/libc/machine/mips/Make.defs.
• Update LDMODULEFLAGS in arch/mips/src/mips32/Toolchain.defs to include the little-endian (-EL) flag.
• Update up_coherent_dcache for proper cache synchronization on JZ4780.

Note: Please adhere to Contributing Guidelines.

Testing

Enable the Module Example and set /dev/sda as the Block driver device path
Build nuttx. (Build used to fail before this change)
Copy ./apps/bin/chardev formated USB stick (chardev is created when nuttx is built)
Plug stick into CI20 USB port

Boot the nuttx image on the CI20 and run "module" to test.

NuttShell (NSH) NuttX-13.0.0
nsh> module
Mounting vfat filesystem at target=/mnt/vfat
module_initialize
chardev_read: Returning 36 bytes
chardev_read: Returning (0x8008fe48):
0000  48 69 20 74 68 65 72 65 2c 20 61 70 70 73 2f 65  Hi there, apps/e
0010  78 61 6d 70 6c 65 73 2f 6d 6f 64 75 6c 65 20 74  xamples/module t
0020  65 73 74 0a                                      est.            
main: Bytes read (0x8008fe48):
0000  48 69 20 74 68 65 72 65 2c 20 61 70 70 73 2f 65  Hi there, apps/e
0010  78 61 6d 70 6c 65 73 2f 6d 6f 64 75 6c 65 20 74  xamples/module t
0020  65 73 74 0a                                      est.            
chardev_write: Writing 26 bytes
chardev_write: Writing (0x80082030):
0000  48 69 20 74 68 65 72 65 20 69 6e 73 74 61 6c 6c  Hi there install
0010  65 64 20 64 72 69 76 65 72 0a                    ed driver.      
main: Bytes written (0x80082030):
0000  48 69 20 74 68 65 72 65 20 69 6e 73 74 61 6c 6c  Hi there install
0010  65 64 20 64 72 69 76 65 72 0a                    ed driver.      
module_uninitialize
main: Read 36 bytes
main: Wrote 26 bytes
nsh> 

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MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb