Update to android-mainline kernel headers v5.4.

Update generate_uapi_headers.sh to checkout the android mainline
kernel. Also, add a small modification to look for the kernel directory
in common not linux-stable.

Remove deprecated android headers from android/uapi/linux. Also,
remove f_accessory.h since it's in the android mainline kernel.

Test: Builds and runs on walleye.
Change-Id: Ia371305e19f56e6bcc2db6d5b4d299819f07ffc6
diff --git a/libc/kernel/uapi/asm-x86/asm/svm.h b/libc/kernel/uapi/asm-x86/asm/svm.h
index 76fb985..4929c13 100644
--- a/libc/kernel/uapi/asm-x86/asm/svm.h
+++ b/libc/kernel/uapi/asm-x86/asm/svm.h
@@ -91,6 +91,7 @@
 #define SVM_EXIT_MWAIT 0x08b
 #define SVM_EXIT_MWAIT_COND 0x08c
 #define SVM_EXIT_XSETBV 0x08d
+#define SVM_EXIT_RDPRU 0x08e
 #define SVM_EXIT_NPF 0x400
 #define SVM_EXIT_AVIC_INCOMPLETE_IPI 0x401
 #define SVM_EXIT_AVIC_UNACCELERATED_ACCESS 0x402