LoongArch: Update Loongson-3 default config file

1. Increase NR_CPUS to 2048.
2. Enable KEXEC_FILE options.
3. Enable some EXT4/XFS options.
4. Enable Loongson PWM/MMC/BMC/SE drivers.
5. Enable simple DRM driver.
6. Enable some Intel ethernet drivers.
7. Enable some gpio drivers.
8. Enable some network options.
9. Enable SM3/SM4 cryptographic algorithms.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>