Kernel: Rework kernel-side ELF loading

ELFs are now loaded as MemoryRegions so they don't need special handling
anywhere. This also allows file backed COW optimizations to work. This
was not the case before.

This patch removes now obsolete LoadableELF and unused ELF files from
LibElf.

kernel/CMakeLists.txt

@@ -22,6 +22,7 @@ set(KERNEL_SOURCES
 	kernel/Device/NullDevice.cpp
 	kernel/Device/RandomDevice.cpp
 	kernel/Device/ZeroDevice.cpp
+	kernel/ELF.cpp
 	kernel/Errors.cpp
 	kernel/FS/DevFS/FileSystem.cpp
 	kernel/FS/Ext2/FileSystem.cpp
@@ -151,10 +152,6 @@ set(KLIBC_SOURCES
 	klibc/string.cpp
 )
 
-set(LIBELF_SOURCES
-	../userspace/libraries/LibELF/LibELF/LoadableELF.cpp
-)
-
 set(LIBFONT_SOURCES
 	../userspace/libraries/LibFont/Font.cpp
 	../userspace/libraries/LibFont/PSF.cpp
@@ -169,7 +166,6 @@ set(KERNEL_SOURCES
 	${KERNEL_SOURCES}
 	${BAN_SOURCES}
 	${KLIBC_SOURCES}
-	${LIBELF_SOURCES}
 	${LIBFONT_SOURCES}
 	${LIBINPUT_SOURCE}
 )