Reduce the number of used unstable features of x86_64 crate

To reduce nightly breakage.

Author: phil-opp

Diff for: Cargo.toml

@@ -29,7 +29,7 @@ required-features = ["uefi_bin"]
 
 [dependencies]
 xmas-elf = { version = "0.6.2", optional = true }
-x86_64 = { version = "0.13.2", optional = true }
+x86_64 = { version = "0.13.2", optional = true, default-features = false, features = ["instructions", "inline_asm"] }
 usize_conversions = { version = "0.2.0", optional = true }
 bit_field = { version = "0.10.0", optional = true }
 log = { version = "0.4.8", optional = true }

Diff for: tests/test_kernels/default_settings/Cargo.toml

@@ -6,5 +6,5 @@ edition = "2018"
 
 [dependencies]
 bootloader = { path = "../../.." }
-x86_64 = "0.13.2"
+x86_64 = { version = "0.13.2", optional = true, default-features = false, features = ["instructions", "inline_asm"] }
 uart_16550 = "0.2.10"

Diff for: tests/test_kernels/map_phys_mem/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2018"
 
 [dependencies]
 bootloader = { path = "../../.." }
-x86_64 = "0.13.2"
+x86_64 = { version = "0.13.2", optional = true, default-features = false, features = ["instructions", "inline_asm"] }
 uart_16550 = "0.2.10"
 
 [package.metadata.bootloader]